The recent discovery of barred spiral galaxies in the early Universe (z > 2) poses questions of how these structures form and
how they influence galaxy evolution in the early Universe. In this study, we investigate the morphology and kinematics of the
far-infrared (FIR) continuum and [C II] emission in BRI1335-0417 at z ≈ 4.4 from ALMA observations. The variations in
position angle and ellipticity of the isophotes show the characteristic signature of a barred galaxy. The bar, 3.3+0.2 −0.2 kpc long in
radius and bridging the previously identified two-armed spiral, is evident in both [C II] and FIR images, driving the galaxy’s rapid
evolution by channelling gas towards the nucleus. Fourier analysis of the [C II] velocity field reveals an unambiguous kinematic
m = 2 mode with a line-of-sight velocity amplitude of up to ∼30–40 km s−1; a plausible explanation is the disc’s vertical bending
mode triggered by external perturbation, which presumably induced the high star formation rate and the bar/spiral structure. The
bar identified in [C II] and FIR images of the gas-rich disc galaxy ( 70 per cent of the total mass within radius R ≈ 2.2 disc
scale lengths) suggests a new perspective of early bar formation in high redshift gas-rich galaxies – a gravitationally unstable
gas-rich disc creating a star-forming gaseous bar, rather than a stellar bar emerging from a pre-existing stellar disc. This may
explain the prevalent bar-like structures seen in FIR images of high-redshift submillimeter galaxies.
UV and Hα HST observations of 6 GASP jellyfish galaxiesSérgio Sacani
Star-forming, Hα-emitting clumps are found embedded in the gaseous tails of galaxies undergoing
intense ram pressure stripping in galaxy clusters, so-called jellyfish galaxies. These clumps offer a
unique opportunity to study star formation under extreme conditions, in the absence of an underlying
disk and embedded within the hot intracluster medium. Yet, a comprehensive, high spatial resolution
study of these systems is missing. We obtained UVIS/HST data to observe the first statistical sample
of clumps in the tails and disks of six jellyfish galaxies from the GASP survey; we used a combination
of broad-band (UV to I) filters and a narrow-band Hα filter. HST observations are needed to study
the sizes, stellar masses and ages of the clumps and their clustering hierarchy. These observations will
be used to study the clump scaling relations, the universality of the star formation process and verify
whether a disk is irrelevant, as hinted by jellyfish galaxy results. This paper presents the observations,
data reduction strategy, and some general results based on the preliminary data analysis. The UVIS
high spatial resolution gives an unprecedented sharp view of the complex structure of the inner regions
of the galaxies and of the substructures in the galaxy disks. We found clear signatures of stripping
in regions very close in projection to the galactic disk. The star-forming regions in the stripped tails
are extremely bright and compact while we did not detect a significant number of star-forming clumps
outside those detected by MUSE. The paper finally presents the development plan for the project.
UV and Hα HST observations of 6 GASP jellyfish galaxiesSérgio Sacani
Star-forming, Hα-emitting clumps are found embedded in the gaseous tails of galaxies undergoing
intense ram pressure stripping in galaxy clusters, so-called jellyfish galaxies. These clumps offer a
unique opportunity to study star formation under extreme conditions, in the absence of an underlying
disk and embedded within the hot intracluster medium. Yet, a comprehensive, high spatial resolution
study of these systems is missing. We obtained UVIS/HST data to observe the first statistical sample
of clumps in the tails and disks of six jellyfish galaxies from the GASP survey; we used a combination
of broad-band (UV to I) filters and a narrow-band Hα filter. HST observations are needed to study
the sizes, stellar masses and ages of the clumps and their clustering hierarchy. These observations will
be used to study the clump scaling relations, the universality of the star formation process and verify
whether a disk is irrelevant, as hinted by jellyfish galaxy results. This paper presents the observations,
data reduction strategy, and some general results based on the preliminary data analysis. The UVIS
high spatial resolution gives an unprecedented sharp view of the complex structure of the inner regions
of the galaxies and of the substructures in the galaxy disks. We found clear signatures of stripping
in regions very close in projection to the galactic disk. The star-forming regions in the stripped tails
are extremely bright and compact while we did not detect a significant number of star-forming clumps
outside those detected by MUSE. The paper finally presents the development plan for the project.
UV and Hα HST observations of 6 GASP jellyfish galaxiesSérgio Sacani
Star-forming, Hα-emitting clumps are found embedded in the gaseous tails of galaxies undergoing
intense ram pressure stripping in galaxy clusters, so-called jellyfish galaxies. These clumps offer a
unique opportunity to study star formation under extreme conditions, in the absence of an underlying
disk and embedded within the hot intracluster medium. Yet, a comprehensive, high spatial resolution
study of these systems is missing. We obtained UVIS/HST data to observe the first statistical sample
of clumps in the tails and disks of six jellyfish galaxies from the GASP survey; we used a combination
of broad-band (UV to I) filters and a narrow-band Hα filter. HST observations are needed to study
the sizes, stellar masses and ages of the clumps and their clustering hierarchy. These observations will
be used to study the clump scaling relations, the universality of the star formation process and verify
whether a disk is irrelevant, as hinted by jellyfish galaxy results. This paper presents the observations,
data reduction strategy, and some general results based on the preliminary data analysis. The UVIS
high spatial resolution gives an unprecedented sharp view of the complex structure of the inner regions
of the galaxies and of the substructures in the galaxy disks. We found clear signatures of stripping
in regions very close in projection to the galactic disk. The star-forming regions in the stripped tails
are extremely bright and compact while we did not detect a significant number of star-forming clumps
outside those detected by MUSE. The paper finally presents the development plan for the project.
HST imaging of star-forming clumps in 6 GASP ram-pressure stripped galaxiesSérgio Sacani
Exploiting broad- and narrow-band images of the Hubble Space Telescope from near-UV to I-band
restframe, we study the star-forming clumps of six galaxies of the GASP sample undergoing strong
ram-pressure stripping (RPS). Clumps are detected in Hα and near-UV, tracing star formation on
different timescales. We consider clumps located in galaxy disks, in the stripped tails and those
formed in stripped gas but still close to the disk, called extraplanar. We detect 2406 Hα-selected
clumps (1708 in disks, 375 in extraplanar regions, and 323 in tails) and 3750 UV-selected clumps (2026
disk clumps, 825 extraplanar clumps and 899 tail clumps). Only ∼ 15% of star-forming clumps are
spatially resolved, meaning that most are smaller than ∼ 140 pc. We study the luminosity and size
distribution functions (LDFs and SDFs, respectively) and the luminosity-size relation. The average
LDF slope is 1.79 ± 0.09, while the average SDF slope is 3.1 ± 0.5. Results suggest the star formation
to be turbulence driven and scale-free, as in main-sequence galaxies. All the clumps, whether they are
in the disks or in the tails, have an enhanced Hα luminosity at a given size, compared to the clumps in
main-sequence galaxies. Indeed, their Hα luminosity is closer to that of clumps in starburst galaxies,
indicating that ram pressure is able to enhance the luminosity. No striking differences are found among
disk and tail clumps, suggesting that the different environments in which they are embedded play a
minor role in influencing the star formation.
HST imaging of star-forming clumps in 6 GASP ram-pressure stripped galaxiesSérgio Sacani
Exploiting broad- and narrow-band images of the Hubble Space Telescope from near-UV to I-band
restframe, we study the star-forming clumps of six galaxies of the GASP sample undergoing strong
ram-pressure stripping (RPS). Clumps are detected in Hα and near-UV, tracing star formation on
different timescales. We consider clumps located in galaxy disks, in the stripped tails and those
formed in stripped gas but still close to the disk, called extraplanar. We detect 2406 Hα-selected
clumps (1708 in disks, 375 in extraplanar regions, and 323 in tails) and 3750 UV-selected clumps (2026
disk clumps, 825 extraplanar clumps and 899 tail clumps). Only ∼ 15% of star-forming clumps are
spatially resolved, meaning that most are smaller than ∼ 140 pc. We study the luminosity and size
distribution functions (LDFs and SDFs, respectively) and the luminosity-size relation. The average
LDF slope is 1.79 ± 0.09, while the average SDF slope is 3.1 ± 0.5. Results suggest the star formation
to be turbulence driven and scale-free, as in main-sequence galaxies. All the clumps, whether they are
in the disks or in the tails, have an enhanced Hα luminosity at a given size, compared to the clumps in
main-sequence galaxies. Indeed, their Hα luminosity is closer to that of clumps in starburst galaxies,
indicating that ram pressure is able to enhance the luminosity. No striking differences are found among
disk and tail clumps, suggesting that the different environments in which they are embedded play a
minor role in influencing the star formation.
HST imaging of star-forming clumps in 6 GASP ram-pressure stripped galaxiesSérgio Sacani
Exploiting broad- and narrow-band images of the Hubble Space Telescope from near-UV to I-band
restframe, we study the star-forming clumps of six galaxies of the GASP sample undergoing strong
ram-pressure stripping (RPS). Clumps are detected in Hα and near-UV, tracing star formation on
different timescales. We consider clumps located in galaxy disks, in the stripped tails and those
formed in stripped gas but still close to the disk, called extraplanar. We detect 2406 Hα-selected
clumps (1708 in disks, 375 in extraplanar regions, and 323 in tails) and 3750 UV-selected clumps (2026
disk clumps, 825 extraplanar clumps and 899 tail clumps). Only ∼ 15% of star-forming clumps are
spatially resolved, meaning that most are smaller than ∼ 140 pc. We study the luminosity and size
distribution functions (LDFs and SDFs, respectively) and the luminosity-size relation. The average
LDF slope is 1.79 ± 0.09, while the average SDF slope is 3.1 ± 0.5. Results suggest the star formation
to be turbulence driven and scale-free, as in main-sequence galaxies. All the clumps, whether they are
in the disks or in the tails, have an enhanced Hα luminosity at a given size, compared to the clumps in
main-sequence galaxies. Indeed, their Hα luminosity is closer to that of clumps in starburst galaxies,
indicating that ram pressure is able to enhance the luminosity. No striking differences are found among
disk and tail clumps, suggesting that the different environments in which they are embedded play a
minor role in influencing the star formation.
The SPHERE view of three interacting twin disc systems in polarised lightSérgio Sacani
Dense stellar environments as hosts of ongoing star formation increase the probability of gravitational encounters among stellar
systems during the early stages of evolution. Stellar interaction may occur through non-recurring, hyperbolic or parabolic passages
(a so-called ‘fly-by’), through secular binary evolution, or through binary capture. In all three scenarios, the strong gravitational
perturbation is expected to manifest itself in the disc structures around the individual stars. Here, we present near-infrared
polarised light observations that were taken with the SPHERE/IRDIS instrument of three known interacting twin-disc systems:
AS 205, EM* SR 24, and FU Orionis. The scattered light exposes spirals likely caused by the gravitational interaction. On
a larger scale, we observe connecting filaments between the stars. We analyse their very complex polarised intensity and put
particular attention to the presence of multiple light sources in these systems. The local angle of linear polarisation indicates
the source whose light dominates the scattering process from the bridging region between the two stars. Further, we show
that the polarised intensity from scattering with multiple relevant light sources results from an incoherent summation of the
individuals’ contribution. This can produce nulls of polarised intensity in an image, as potentially observed in AS 205.We discuss
the geometry and content of the systems by comparing the polarised light observations with other data at similar resolution,
namely with ALMA continuum and gas emission. Collective observational data can constrain the systems’ geometry and stellar
trajectories, with the important potential to differentiate between dynamical scenarios of stellar interaction.
A High-mass, Young Star-forming Core Escaping from Its Parental FilamentSérgio Sacani
We studied the unique kinematic properties in massive filament G352.63-1.07 at 103 au spatial scale with the dense
molecular tracers observed with the Atacama Large Millimeter/submillimeter Array. We find the central massive
core M1 (12 Me) being separated from the surrounding filament with a velocity difference of
- =- - v vsys 2 km s 1 and a transverse separation within 3″. Meanwhile, as shown in multiple dense-gas
tracers, M1 has a spatial extension closely aligned with the main filament and is connected to the filament toward
both its ends. M1 thus represents a very beginning state for a massive, young star-forming core escaping from the
parental filament, within a timescale of ∼4000 yr. Based on its kinetic energy (3.5 × 1044 erg), the core escape is
unlikely solely due to the original filament motion or magnetic field but requires more energetic events such as a
rapid intense anisotropic collapse. The released energy also seems to noticeably increase the environmental
turbulence. This may help the filament to become stabilized again.
UV and Hα HST observations of 6 GASP jellyfish galaxiesSérgio Sacani
Star-forming, Hα-emitting clumps are found embedded in the gaseous tails of galaxies undergoing
intense ram pressure stripping in galaxy clusters, so-called jellyfish galaxies. These clumps offer a
unique opportunity to study star formation under extreme conditions, in the absence of an underlying
disk and embedded within the hot intracluster medium. Yet, a comprehensive, high spatial resolution
study of these systems is missing. We obtained UVIS/HST data to observe the first statistical sample
of clumps in the tails and disks of six jellyfish galaxies from the GASP survey; we used a combination
of broad-band (UV to I) filters and a narrow-band Hα filter. HST observations are needed to study
the sizes, stellar masses and ages of the clumps and their clustering hierarchy. These observations will
be used to study the clump scaling relations, the universality of the star formation process and verify
whether a disk is irrelevant, as hinted by jellyfish galaxy results. This paper presents the observations,
data reduction strategy, and some general results based on the preliminary data analysis. The UVIS
high spatial resolution gives an unprecedented sharp view of the complex structure of the inner regions
of the galaxies and of the substructures in the galaxy disks. We found clear signatures of stripping
in regions very close in projection to the galactic disk. The star-forming regions in the stripped tails
are extremely bright and compact while we did not detect a significant number of star-forming clumps
outside those detected by MUSE. The paper finally presents the development plan for the project.
UV and Hα HST observations of 6 GASP jellyfish galaxiesSérgio Sacani
Star-forming, Hα-emitting clumps are found embedded in the gaseous tails of galaxies undergoing
intense ram pressure stripping in galaxy clusters, so-called jellyfish galaxies. These clumps offer a
unique opportunity to study star formation under extreme conditions, in the absence of an underlying
disk and embedded within the hot intracluster medium. Yet, a comprehensive, high spatial resolution
study of these systems is missing. We obtained UVIS/HST data to observe the first statistical sample
of clumps in the tails and disks of six jellyfish galaxies from the GASP survey; we used a combination
of broad-band (UV to I) filters and a narrow-band Hα filter. HST observations are needed to study
the sizes, stellar masses and ages of the clumps and their clustering hierarchy. These observations will
be used to study the clump scaling relations, the universality of the star formation process and verify
whether a disk is irrelevant, as hinted by jellyfish galaxy results. This paper presents the observations,
data reduction strategy, and some general results based on the preliminary data analysis. The UVIS
high spatial resolution gives an unprecedented sharp view of the complex structure of the inner regions
of the galaxies and of the substructures in the galaxy disks. We found clear signatures of stripping
in regions very close in projection to the galactic disk. The star-forming regions in the stripped tails
are extremely bright and compact while we did not detect a significant number of star-forming clumps
outside those detected by MUSE. The paper finally presents the development plan for the project.
UV and Hα HST observations of 6 GASP jellyfish galaxiesSérgio Sacani
Star-forming, Hα-emitting clumps are found embedded in the gaseous tails of galaxies undergoing
intense ram pressure stripping in galaxy clusters, so-called jellyfish galaxies. These clumps offer a
unique opportunity to study star formation under extreme conditions, in the absence of an underlying
disk and embedded within the hot intracluster medium. Yet, a comprehensive, high spatial resolution
study of these systems is missing. We obtained UVIS/HST data to observe the first statistical sample
of clumps in the tails and disks of six jellyfish galaxies from the GASP survey; we used a combination
of broad-band (UV to I) filters and a narrow-band Hα filter. HST observations are needed to study
the sizes, stellar masses and ages of the clumps and their clustering hierarchy. These observations will
be used to study the clump scaling relations, the universality of the star formation process and verify
whether a disk is irrelevant, as hinted by jellyfish galaxy results. This paper presents the observations,
data reduction strategy, and some general results based on the preliminary data analysis. The UVIS
high spatial resolution gives an unprecedented sharp view of the complex structure of the inner regions
of the galaxies and of the substructures in the galaxy disks. We found clear signatures of stripping
in regions very close in projection to the galactic disk. The star-forming regions in the stripped tails
are extremely bright and compact while we did not detect a significant number of star-forming clumps
outside those detected by MUSE. The paper finally presents the development plan for the project.
HST imaging of star-forming clumps in 6 GASP ram-pressure stripped galaxiesSérgio Sacani
Exploiting broad- and narrow-band images of the Hubble Space Telescope from near-UV to I-band
restframe, we study the star-forming clumps of six galaxies of the GASP sample undergoing strong
ram-pressure stripping (RPS). Clumps are detected in Hα and near-UV, tracing star formation on
different timescales. We consider clumps located in galaxy disks, in the stripped tails and those
formed in stripped gas but still close to the disk, called extraplanar. We detect 2406 Hα-selected
clumps (1708 in disks, 375 in extraplanar regions, and 323 in tails) and 3750 UV-selected clumps (2026
disk clumps, 825 extraplanar clumps and 899 tail clumps). Only ∼ 15% of star-forming clumps are
spatially resolved, meaning that most are smaller than ∼ 140 pc. We study the luminosity and size
distribution functions (LDFs and SDFs, respectively) and the luminosity-size relation. The average
LDF slope is 1.79 ± 0.09, while the average SDF slope is 3.1 ± 0.5. Results suggest the star formation
to be turbulence driven and scale-free, as in main-sequence galaxies. All the clumps, whether they are
in the disks or in the tails, have an enhanced Hα luminosity at a given size, compared to the clumps in
main-sequence galaxies. Indeed, their Hα luminosity is closer to that of clumps in starburst galaxies,
indicating that ram pressure is able to enhance the luminosity. No striking differences are found among
disk and tail clumps, suggesting that the different environments in which they are embedded play a
minor role in influencing the star formation.
HST imaging of star-forming clumps in 6 GASP ram-pressure stripped galaxiesSérgio Sacani
Exploiting broad- and narrow-band images of the Hubble Space Telescope from near-UV to I-band
restframe, we study the star-forming clumps of six galaxies of the GASP sample undergoing strong
ram-pressure stripping (RPS). Clumps are detected in Hα and near-UV, tracing star formation on
different timescales. We consider clumps located in galaxy disks, in the stripped tails and those
formed in stripped gas but still close to the disk, called extraplanar. We detect 2406 Hα-selected
clumps (1708 in disks, 375 in extraplanar regions, and 323 in tails) and 3750 UV-selected clumps (2026
disk clumps, 825 extraplanar clumps and 899 tail clumps). Only ∼ 15% of star-forming clumps are
spatially resolved, meaning that most are smaller than ∼ 140 pc. We study the luminosity and size
distribution functions (LDFs and SDFs, respectively) and the luminosity-size relation. The average
LDF slope is 1.79 ± 0.09, while the average SDF slope is 3.1 ± 0.5. Results suggest the star formation
to be turbulence driven and scale-free, as in main-sequence galaxies. All the clumps, whether they are
in the disks or in the tails, have an enhanced Hα luminosity at a given size, compared to the clumps in
main-sequence galaxies. Indeed, their Hα luminosity is closer to that of clumps in starburst galaxies,
indicating that ram pressure is able to enhance the luminosity. No striking differences are found among
disk and tail clumps, suggesting that the different environments in which they are embedded play a
minor role in influencing the star formation.
HST imaging of star-forming clumps in 6 GASP ram-pressure stripped galaxiesSérgio Sacani
Exploiting broad- and narrow-band images of the Hubble Space Telescope from near-UV to I-band
restframe, we study the star-forming clumps of six galaxies of the GASP sample undergoing strong
ram-pressure stripping (RPS). Clumps are detected in Hα and near-UV, tracing star formation on
different timescales. We consider clumps located in galaxy disks, in the stripped tails and those
formed in stripped gas but still close to the disk, called extraplanar. We detect 2406 Hα-selected
clumps (1708 in disks, 375 in extraplanar regions, and 323 in tails) and 3750 UV-selected clumps (2026
disk clumps, 825 extraplanar clumps and 899 tail clumps). Only ∼ 15% of star-forming clumps are
spatially resolved, meaning that most are smaller than ∼ 140 pc. We study the luminosity and size
distribution functions (LDFs and SDFs, respectively) and the luminosity-size relation. The average
LDF slope is 1.79 ± 0.09, while the average SDF slope is 3.1 ± 0.5. Results suggest the star formation
to be turbulence driven and scale-free, as in main-sequence galaxies. All the clumps, whether they are
in the disks or in the tails, have an enhanced Hα luminosity at a given size, compared to the clumps in
main-sequence galaxies. Indeed, their Hα luminosity is closer to that of clumps in starburst galaxies,
indicating that ram pressure is able to enhance the luminosity. No striking differences are found among
disk and tail clumps, suggesting that the different environments in which they are embedded play a
minor role in influencing the star formation.
The SPHERE view of three interacting twin disc systems in polarised lightSérgio Sacani
Dense stellar environments as hosts of ongoing star formation increase the probability of gravitational encounters among stellar
systems during the early stages of evolution. Stellar interaction may occur through non-recurring, hyperbolic or parabolic passages
(a so-called ‘fly-by’), through secular binary evolution, or through binary capture. In all three scenarios, the strong gravitational
perturbation is expected to manifest itself in the disc structures around the individual stars. Here, we present near-infrared
polarised light observations that were taken with the SPHERE/IRDIS instrument of three known interacting twin-disc systems:
AS 205, EM* SR 24, and FU Orionis. The scattered light exposes spirals likely caused by the gravitational interaction. On
a larger scale, we observe connecting filaments between the stars. We analyse their very complex polarised intensity and put
particular attention to the presence of multiple light sources in these systems. The local angle of linear polarisation indicates
the source whose light dominates the scattering process from the bridging region between the two stars. Further, we show
that the polarised intensity from scattering with multiple relevant light sources results from an incoherent summation of the
individuals’ contribution. This can produce nulls of polarised intensity in an image, as potentially observed in AS 205.We discuss
the geometry and content of the systems by comparing the polarised light observations with other data at similar resolution,
namely with ALMA continuum and gas emission. Collective observational data can constrain the systems’ geometry and stellar
trajectories, with the important potential to differentiate between dynamical scenarios of stellar interaction.
A High-mass, Young Star-forming Core Escaping from Its Parental FilamentSérgio Sacani
We studied the unique kinematic properties in massive filament G352.63-1.07 at 103 au spatial scale with the dense
molecular tracers observed with the Atacama Large Millimeter/submillimeter Array. We find the central massive
core M1 (12 Me) being separated from the surrounding filament with a velocity difference of
- =- - v vsys 2 km s 1 and a transverse separation within 3″. Meanwhile, as shown in multiple dense-gas
tracers, M1 has a spatial extension closely aligned with the main filament and is connected to the filament toward
both its ends. M1 thus represents a very beginning state for a massive, young star-forming core escaping from the
parental filament, within a timescale of ∼4000 yr. Based on its kinetic energy (3.5 × 1044 erg), the core escape is
unlikely solely due to the original filament motion or magnetic field but requires more energetic events such as a
rapid intense anisotropic collapse. The released energy also seems to noticeably increase the environmental
turbulence. This may help the filament to become stabilized again.
Asymmetrical tidal tails of open star clusters: stars crossing their cluster’...Sérgio Sacani
The document discusses asymmetrical tidal tails observed around five open star clusters, which challenges Newtonian gravity. It summarizes how tidal tails form as stars escape clusters due to energy equipartition. Observations of the Hyades, Praesepe, Coma Berenices, COIN-Gaia 13, and NGC 752 clusters found more stars in the leading tidal tails within 50 pc of the clusters. Simulations show that in Newtonian gravity, tidal tails should be symmetrical, but asymmetries can arise in Milgromian dynamics. Future work is needed to better map tidal tails and develop Milgromian simulations.
The debris of the ‘last major merger’ is dynamically youngSérgio Sacani
The Milky Way’s (MW) inner stellar halo contains an [Fe/H]-rich component with highly eccentric orbits, often referred to as the
‘last major merger.’ Hypotheses for the origin of this component include Gaia-Sausage/Enceladus (GSE), where the progenitor
collided with the MW proto-disc 8–11 Gyr ago, and the Virgo Radial Merger (VRM), where the progenitor collided with the
MW disc within the last 3 Gyr. These two scenarios make different predictions about observable structure in local phase space,
because the morphology of debris depends on how long it has had to phase mix. The recently identified phase-space folds in Gaia
DR3 have positive caustic velocities, making them fundamentally different than the phase-mixed chevrons found in simulations
at late times. Roughly 20 per cent of the stars in the prograde local stellar halo are associated with the observed caustics. Based
on a simple phase-mixing model, the observed number of caustics are consistent with a merger that occurred 1–2 Gyr ago.
We also compare the observed phase-space distribution to FIRE-2 Latte simulations of GSE-like mergers, using a quantitative
measurement of phase mixing (2D causticality). The observed local phase-space distribution best matches the simulated data
1–2 Gyr after collision, and certainly not later than 3 Gyr. This is further evidence that the progenitor of the ‘last major merger’
did not collide with the MW proto-disc at early times, as is thought for the GSE, but instead collided with the MW disc within
the last few Gyr, consistent with the body of work surrounding the VRM.
Stellar-mass black holes in the Hyades star cluster?Sérgio Sacani
Astrophysical models of binary-black hole mergers in the Universe require a significant fraction of stellar-mass black holes (BHs)
to receive negligible natal kicks to explain the gravitational wave detections. This implies that BHs should be retained even in
open clusters with low escape velocities (≲ 1 km/s). We search for signatures of the presence of BHs in the nearest open cluster
to the Sun – the Hyades – by comparing density profiles of direct 𝑁-body models to data from Gaia. The observations are best
reproduced by models with 2−3 BHs at present. Models that never possessed BHs have an half-mass radius ∼ 30% smaller than
the observed value, while those where the last BHs were ejected recently (≲ 150 Myr ago) can still reproduce the density profile.
In 50% of the models hosting BHs, we find BHs with stellar companion(s). Their period distribution peaks at ∼ 103 yr, making
them unlikely to be found through velocity variations. We look for potential BH companions through large Gaia astrometric and
spectroscopic errors, identifying 56 binary candidates - none of which consistent with a massive compact companion. Models
with 2 − 3 BHs have an elevated central velocity dispersion, but observations can not yet discriminate. We conclude that the
present-day structure of the Hyades requires a significant fraction of BHs to receive natal kicks smaller than the escape velocity
of ∼ 3 km s−1
at the time of BH formation and that the nearest BHs to the Sun are in, or near, Hyades.
Collimation of the Relativistic Jet in the Quasar 3C273Sérgio Sacani
The collimation of relativistic jets launched from the vicinity of supermassive black holes (SMBHs) at the centers
of active galactic nuclei (AGNs) is one of the key questions to understand the nature of AGN jets. However, little is
known about the detailed jet structure for AGN like quasars since very high angular resolutions are required to
resolve these objects. We present very long baseline interferometry (VLBI) observations of the archetypical quasar
3C 273 at 86 GHz, performed with the Global Millimeter VLBI Array, for the first time including the Atacama
Large Millimeter/submillimeter Array. Our observations achieve a high angular resolution down to ∼60 μas,
resolving the innermost part of the jet ever on scales of ∼105 Schwarzschild radii. Our observations, including
close-in-time High Sensitivity Array observations of 3C 273 at 15, 22, and 43 GHz, suggest that the inner jet
collimates parabolically, while the outer jet expands conically, similar to jets from other nearby low-luminosity
AGNs. We discovered the jet collimation break around 107 Schwarzschild radii, providing the first compelling
evidence for structural transition in a quasar jet. The location of the collimation break for 3C 273 is farther
downstream from the sphere of gravitational influence (SGI) from the central SMBH. With the results for other
AGN jets, our results show that the end of the collimation zone in AGN jets is governed not only by the SGI of the
SMBH but also by the more diverse properties of the central nuclei.
Formation of low mass protostars and their circumstellar disksSérgio Sacani
Understanding circumstellar disks is of prime importance in astrophysics, however, their birth process remains poorly constrained due to observational and numerical challenges. Recent numerical works have shown that the small-scale physics, often wrapped into a sub-grid model, play a crucial role in disk formation and evolution. This calls for a combined approach in which both the protostar and circumstellar disk are studied in concert. Aims. We aim to elucidate the small scale physics and constrain sub-grid parameters commonly chosen in the literature by resolving the star-disk interaction. Methods. We carry out a set of very high resolution 3D radiative-hydrodynamics simulations that self-consistently describe the collapse of a turbulent dense molecular cloud core to stellar densities. We study the birth of the protostar, the circumstellar disk, and its early evolution (< 6 yr after protostellar formation). Results. Following the second gravitational collapse, the nascent protostar quickly reaches breakup velocity and sheds its surface material, thus forming a hot (∼ 103 K), dense, and highly flared circumstellar disk. The protostar is embedded within the disk, such that material can flow without crossing any shock fronts. The circumstellar disk mass quickly exceeds that of the protostar, and its kinematics are dominated by self-gravity. Accretion onto the disk is highly anisotropic, and accretion onto the protostar mainly occurs through material that slides on the disk surface. The polar mass flux is negligible in comparison. The radiative behavior also displays a strong anisotropy, as the polar accretion shock is shown to be supercritical whereas its equatorial counterpart is subcritical. We also f ind a remarkable convergence of our results with respect to initial conditions. Conclusions. These results reveal the structure and kinematics in the smallest spatial scales relevant to protostellar and circumstellar disk evolution. They can be used to describe accretion onto regions commonly described by sub-grid models in simulations studying larger scale physics.
Detection of anisotropic satellite quenching in galaxy clusters up to z ∼ 1Sérgio Sacani
Satellite galaxies in the cluster environment are more likely to be quenched than galaxies in the general field. Recently, it has
been reported that satellite galaxy quenching depends on the orientation relative to their central galaxies: satellites along the
major axis of centrals are more likely to be quenched than those along the minor axis. In this paper, we report a detection
of such anisotropic quenching up to z ∼ 1 based on a large optically selected cluster catalogue constructed from the Hyper
Suprime-Cam Subaru Strategic Program. We calculate the quiescent satellite galaxy fraction as a function of orientation angle
measured from the major axis of central galaxies and find that the quiescent fractions at 0.25 < z < 1 are reasonably fitted
by sinusoidal functions with amplitudes of a few per cent. Anisotropy is clearer in inner regions (<r200m) of clusters and not
significant in cluster outskirts (>r200m). We also confirm that the observed anisotropy cannot be explained by differences in
local galaxy density or stellar mass distribution along the two axes. Quiescent fraction excesses between the two axes suggest
that the quenching efficiency contributing to the anisotropy is almost independent of stellar mass, at least down to our stellar
mass limit of M∗ = 1 × 1010 M. Finally, we argue that the physical origins of the observed anisotropy should have shorter
quenching time-scales than ∼ 1 Gyr, like ram-pressure stripping, because, for anisotropic quenching to be observed, satellites
must be quenched before their initial orientation angles are significantly changed.
Kinematics and simulations_of_the_stellar_stream_in_the_halo_of_the_umbrella_...Sérgio Sacani
This document summarizes a study of the stellar stream and substructures around the Umbrella Galaxy (NGC 4651). Deep imaging and spectroscopy were used to characterize the properties and kinematics of the stream. Tracer objects like globular clusters and planetary nebulae were identified and found to delineate a kinematically cold feature in position-velocity space. Dynamical modeling suggests the stream originated from the tidal disruption of a dwarf galaxy on a highly eccentric orbit about 6-10 billion years ago. This work demonstrates the feasibility of using discrete tracers to recover the kinematics and model the dynamics of low surface brightness stellar streams around distant galaxies.
Galaxy interactions are the dominant trigger for local type 2 quasarsSérgio Sacani
The triggering mechanism for the most luminous, quasar-like active galactic nuclei (AGN) remains a source of debate, with
some studies favouring triggering via galaxy mergers, but others finding little evidence to support this mechanism. Here, we
present deep Isaac Newton Telescope/Wide Field Camera imaging observations of a complete sample of 48 optically selected
type 2 quasars – the QSOFEED sample (L[O III] > 108.5 L; z < 0.14). Based on visual inspection by eight classifiers, we find
clear evidence that galaxy interactions are the dominant triggering mechanism for quasar activity in the local universe, with
65+6
−7 per cent of the type 2 quasar hosts showing morphological features consistent with galaxy mergers or encounters, compared
with only 22+5
−4 per cent of a stellar-mass- and redshift-matched comparison sample of non-AGN galaxies – a 5σ difference. The
type 2 quasar hosts are a factor of 3.0+0.5 −0.8 more likely to be morphologically disturbed than their matched non-AGN counterparts,
similar to our previous results for powerful 3CR radio AGN of comparable [O III] emission-line luminosity and redshift. In
contrast to the idea that quasars are triggered at the peaks of galaxy mergers as the two nuclei coalesce, and only become
visible post-coalescence, the majority of morphologically disturbed type 2 quasar sources in our sample are observed in the
pre-coalescence phase (61+8
−9 per cent). We argue that much of the apparent ambiguity that surrounds observational results in this
field is a result of differences in the surface brightness depths of the observations, combined with the effects of cosmological
surface brightness dimming.
The Expansion of the X-Ray Nebula Around η CarSérgio Sacani
1. The author analyzes over 20 years of Chandra X-ray images to measure for the first time the expansion of the X-ray nebula around η Carinae.
2. A combined Chandra image reveals a faint, nearly uniform elliptical shell surrounding the X-ray bright ring, with a similar orientation and shape as the Homunculus nebula but about 3 times larger.
3. The author measures proper motions of brighter regions associated with the X-ray emitting ring, such as the S-ridge and W-arc. Motions are consistent with optical studies of ejecta from the 1840s Great Eruption.
We present the 2020 version of the Siena Galaxy Atlas (SGA-2020), a multiwavelength optical and infrared
imaging atlas of 383,620 nearby galaxies. The SGA-2020 uses optical grz imaging over ≈20,000 deg2 from the
Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys Data Release 9 and infrared imaging in
four bands (spanning 3.4–22 μm) from the 6 year unWISE coadds; it is more than 95% complete for galaxies larger
than R(26) ≈ 25″ and r < 18 measured at the 26 mag arcsec−2 isophote in the r band. The atlas delivers precise
coordinates, multiwavelength mosaics, azimuthally averaged optical surface-brightness profiles, model images and
photometry, and additional ancillary metadata for the full sample. Coupled with existing and forthcoming optical
spectroscopy from the DESI, the SGA-2020 will facilitate new detailed studies of the star formation and mass
assembly histories of nearby galaxies; enable precise measurements of the local velocity field via the Tully–Fisher
and fundamental plane relations; serve as a reference sample of lasting legacy value for time-domain and
multimessenger astronomical events; and more.
A giant thin stellar stream in the Coma Galaxy ClusterSérgio Sacani
The study of dynamically cold stellar streams reveals information about the gravitational potential where they reside and provides
important constraints on the properties of dark matter. However, the intrinsic faintness of these streams makes their detection beyond
Local environments highly challenging. Here, we report the detection of an extremely faint stellar stream (µg,max = 29.5 mag arcsec−2
)
with an extraordinarily coherent and thin morphology in the Coma Galaxy Cluster. This Giant Coma Stream spans ∼510 kpc in length
and appears as a free-floating structure located at a projected distance of 0.8 Mpc from the center of Coma. We do not identify any
potential galaxy remnant or core, and the stream structure appears featureless in our data. We interpret the Giant Coma Stream as
being a recently accreted, tidally disrupting passive dwarf. Using the Illustris-TNG50 simulation, we identify a case with similar
characteristics, showing that, although rare, these types of streams are predicted to exist in Λ-CDM. Our work unveils the presence
of free-floating, extremely faint and thin stellar streams in galaxy clusters, widening the environmental context in which these objects
are found ahead of their promising future application in the study of the properties of dark matter.
AT2023fhn (the Finch): a Luminous Fast Blue Optical Transient at a large offs...Sérgio Sacani
Luminous Fast Blue Optical Transients (LFBOTs) - the prototypical example being AT 2018cow - are a rare class of events
whose origins are poorly understood. They are characterised by rapid evolution, featureless blue spectra at early times, and
luminous X-ray and radio emission. LFBOTs thus far have been found exclusively at small projected offsets from star-forming
host galaxies. We present Hubble Space Telescope, Gemini, Chandra and Very Large Array observations of a new LFBOT,
AT 2023fhn. The Hubble Space Telescope data reveal a large offset (> 3.5 half-light radii) from the two closest galaxies, both
at redshift 𝑧 ∼ 0.24. The location of AT 2023fhn is in stark contrast with previous events, and demonstrates that LFBOTs can
occur in a range of galactic environments.
Triple Spiral Arms of a Triple Protostar System Imaged in Molecular LinesSérgio Sacani
Most stars form in multiple-star systems. For a better understanding of their formation processes, it is important to
resolve the individual protostellar components and the surrounding envelope and disk material at the earliest
possible formation epoch, because the formation history can be lost in a few orbital timescales. Here we present
Atacama Large Millimeter/submillimeter Array observational results of a young multiple protostellar system,
IRAS 04239+2436, where three well-developed large spiral arms were detected in the shocked SO emission.
Along the most conspicuous arm, the accretion streamer was also detected in the SO2 emission. The observational
results are complemented by numerical magnetohydrodynamic simulations, where those large arms only appear in
magnetically weakened clouds. Numerical simulations also suggest that the large triple spiral arms are the result of
gravitational interactions between compact triple protostars and the turbulent infalling envelope.
The galaxy morphology–density relation in the EAGLE simulationSérgio Sacani
This study uses a convolutional neural network trained on observed galaxy images to classify galaxies in the EAGLE cosmological hydrodynamical simulation by visual morphology. It finds that EAGLE reproduces both the observed relationships between galaxy morphology and local density (the morphology-density relation), and between morphology and galaxy mass. Through analysis of the simulations, the key processes identified as driving the morphology-density relation are: (1) the transformation of disc galaxies into lenticular galaxies via gas stripping in dense environments, (2) the formation of lenticular galaxies through merger-induced black hole feedback in less dense environments, and (3) the increasing fraction of more elliptical, high-mass galaxies at higher densities.
How to tell an accreting boson star from a black hole h. olivares et al (2020)SOCIEDAD JULIO GARAVITO
Abstract
The tentative evidences for late time “echoes” in LIGO gravitational
waves (GWs) have been claimed to be signatures of horizonless compact
objects rather than vacuum black holes (BHs) possessing horizons. In
general, in the past, many authors have considered the possibility that
the so-called BHs might be only BH mimickers (BHMs). And recently
it has been suggested that the true astrophysical BH having no intrinsic
magnetic fields may be differentiated from magnetized BHMs by studying
the radial variations of magnetic fields around pertinent compact objects
(Lobanov, Nat. Astron. 2017). Here we highlight that close to the surface
of BHMs, the magnetic field pattern differs significantly from the same for
non-relativistic Neutron Stars (B ∼ r −3 ). In particular, we point out that
for ultra- compact BHMs, the polar field is weaker than the equatorial field
1by an extremely large factor of ∼ z s /lnz s , where z s ≫ 1 is the surface
gravitational redshift. We suggest that by studying the of radial variation
as well as such significant asymmetry of magnetic field structure near the
compact object, future observations may differentiate a theoretical black
hole from a astrophysical BH mimicker (a compact object). This study
also shows that even if some BHMs would be hypothesized to possess
magnetic fields even stronger than that of magnetars, in certain cases, they
may effectively behave as atoll type neutron stars possessing extremely low
magnetic fields.
Keywords: X-ray Binaries; Active Galactic Nuclei; Magnetic Field;
Black Hole Mimickers; Relativistic Astrophysics.
PACS numbers: 04.40.Dg, 97.80.Jp, 97.60.Gb, 95.86.Nv.
Dust Enrichment and Grain Growth in a Smooth Disk around the DG Tau Protostar...Sérgio Sacani
Characterizing the physical properties of dust grains in a protoplanetary disk is critical to comprehending the planet
formation process. Our study presents Atacama Large Millimeter/submillimeter Array (ALMA) high-resolution
observations of the young protoplanetary disk around DG Tau at a 1.3 mm dust continuum. The observations, with
a spatial resolution of ≈0 04, or ≈5 au, revealed a geometrically thin and smooth disk without substantial
substructures, suggesting that the disk retains the initial conditions of the planet formation. To further analyze the
distributions of dust surface density, temperature, and grain size, we conducted a multiband analysis with several
dust models, incorporating ALMA archival data of the 0.87 and 3.1 mm dust polarization. The results showed that
the Toomre Q parameter is 2 at a 20 au radius, assuming a dust-to-gas mass ratio of 0.01. This implies that a
higher dust-to-gas mass ratio is necessary to stabilize the disk. The grain sizes depend on the dust models, and for
the DSHARP compact dust, they were found to be smaller than ∼400 μm in the inner region (r 20 au) while
exceeding larger than 3 mm in the outer part. Radiative transfer calculations show that the dust scale height is lower
than at least one-third of the gas scale height. These distributions of dust enrichment, grain sizes, and weak
turbulence strength may have significant implications for the formation of planetesimals through mechanisms such
as streaming instability. We also discuss the CO snowline effect and collisional fragmentation in dust coagulation
for the origin of the dust size distribution.
The SAMI Galaxy Sur v ey: galaxy spin is more strongly correlated with stella...Sérgio Sacani
We use the SAMI Galaxy Surv e y to examine the drivers of galaxy spin, λR e , in a multidimensional parameter space including stellar mass, stellar population age (or specific star formation rate), and various environmental metrics (local density, halo mass, satellite versus central). Using a partial correlation analysis, we consistently find that age or specific star formation rate is the primary parameter correlating with spin. Light-weighted age and specific star formation rate are more strongly correlated with spin than mass-weighted age. In fact, across our sample, once the relation between light-weighted age and spin is accounted for, there is no significant residual correlation between spin and mass, or spin and environment. This result is strongly suggestive that the present-day environment only indirectly influences spin, via the removal of gas and star formation quenching. That is, environment affects age, then age affects spin. Older galaxies then have lower spin, either due to stars being born dynamically hotter at high redshift, or due to secular heating. Our results appear to rule out environmentally dependent dynamical heating (e.g. g alaxy–g alaxy interactions) being important, at least within 1 R e where our kinematic measurements are made. The picture is more complex when we only consider high-mass galaxies ( M ∗ ≳ 10 11 M ). While the age-spin relation is still strong for these high-mass galaxies, there is a residual environmental trend with central galaxies preferentially having lower spin, compared to satellites of the same age and mass. We argue that this trend is likely due to central galaxies being a preferred location for mergers.
Betelgeuse as a Merger of a Massive Star with a CompanionSérgio Sacani
This document summarizes a study that uses 3D hydrodynamic simulations and 1D stellar evolution modeling to investigate the merger of a 16 solar mass star with a 4 solar mass companion star. The simulations show the companion spirals inward and merges with the primary star's helium core. Approximately 0.6 solar masses of material is ejected in an asymmetric, bipolar outflow. The post-merger structure is then modeled in 1D stellar evolution, showing in some cases the star evolves to have surface properties similar to Betelgeus, with rapid rotation and enhanced nitrogen at the surface. This pioneering study aims to comprehensively model stellar mergers across dynamical, thermal, and nuclear evolutionary timescales.
Candidate young stellar objects in the S-cluster: Kinematic analysis of a sub...Sérgio Sacani
Context. The observation of several L-band emission sources in the S cluster has led to a rich discussion of their nature. However, a definitive answer to the classification of the dusty objects requires an explanation for the detection of compact Doppler-shifted Brγ emission. The ionized hydrogen in combination with the observation of mid-infrared L-band continuum emission suggests that most of these sources are embedded in a dusty envelope. These embedded sources are part of the S-cluster, and their relationship to the S-stars is still under debate. To date, the question of the origin of these two populations has been vague, although all explanations favor migration processes for the individual cluster members. Aims. This work revisits the S-cluster and its dusty members orbiting the supermassive black hole SgrA* on bound Keplerian orbits from a kinematic perspective. The aim is to explore the Keplerian parameters for patterns that might imply a nonrandom distribution of the sample. Additionally, various analytical aspects are considered to address the nature of the dusty sources. Methods. Based on the photometric analysis, we estimated the individual H−K and K−L colors for the source sample and compared the results to known cluster members. The classification revealed a noticeable contrast between the S-stars and the dusty sources. To fit the flux-density distribution, we utilized the radiative transfer code HYPERION and implemented a young stellar object Class I model. We obtained the position angle from the Keplerian fit results; additionally, we analyzed the distribution of the inclinations and the longitudes of the ascending node. Results. The colors of the dusty sources suggest a stellar nature consistent with the spectral energy distribution in the near and midinfrared domains. Furthermore, the evaporation timescales of dusty and gaseous clumps in the vicinity of SgrA* are much shorter ( 2yr) than the epochs covered by the observations (≈15yr). In addition to the strong evidence for the stellar classification of the D-sources, we also find a clear disk-like pattern following the arrangements of S-stars proposed in the literature. Furthermore, we find a global intrinsic inclination for all dusty sources of 60 ± 20◦, implying a common formation process. Conclusions. The pattern of the dusty sources manifested in the distribution of the position angles, inclinations, and longitudes of the ascending node strongly suggests two different scenarios: the main-sequence stars and the dusty stellar S-cluster sources share a common formation history or migrated with a similar formation channel in the vicinity of SgrA*. Alternatively, the gravitational influence of SgrA* in combination with a massive perturber, such as a putative intermediate mass black hole in the IRS 13 cluster, forces the dusty objects and S-stars to follow a particular orbital arrangement. Key words. stars: black holes– stars: formation– Galaxy: center– galaxies: star formation
SDSS1335+0728: The awakening of a ∼ 106M⊙ black hole⋆Sérgio Sacani
Context. The early-type galaxy SDSS J133519.91+072807.4 (hereafter SDSS1335+0728), which had exhibited no prior optical variations during the preceding two decades, began showing significant nuclear variability in the Zwicky Transient Facility (ZTF) alert stream from December 2019 (as ZTF19acnskyy). This variability behaviour, coupled with the host-galaxy properties, suggests that SDSS1335+0728 hosts a ∼ 106M⊙ black hole (BH) that is currently in the process of ‘turning on’. Aims. We present a multi-wavelength photometric analysis and spectroscopic follow-up performed with the aim of better understanding the origin of the nuclear variations detected in SDSS1335+0728. Methods. We used archival photometry (from WISE, 2MASS, SDSS, GALEX, eROSITA) and spectroscopic data (from SDSS and LAMOST) to study the state of SDSS1335+0728 prior to December 2019, and new observations from Swift, SOAR/Goodman, VLT/X-shooter, and Keck/LRIS taken after its turn-on to characterise its current state. We analysed the variability of SDSS1335+0728 in the X-ray/UV/optical/mid-infrared range, modelled its spectral energy distribution prior to and after December 2019, and studied the evolution of its UV/optical spectra. Results. From our multi-wavelength photometric analysis, we find that: (a) since 2021, the UV flux (from Swift/UVOT observations) is four times brighter than the flux reported by GALEX in 2004; (b) since June 2022, the mid-infrared flux has risen more than two times, and the W1−W2 WISE colour has become redder; and (c) since February 2024, the source has begun showing X-ray emission. From our spectroscopic follow-up, we see that (i) the narrow emission line ratios are now consistent with a more energetic ionising continuum; (ii) broad emission lines are not detected; and (iii) the [OIII] line increased its flux ∼ 3.6 years after the first ZTF alert, which implies a relatively compact narrow-line-emitting region. Conclusions. We conclude that the variations observed in SDSS1335+0728 could be either explained by a ∼ 106M⊙ AGN that is just turning on or by an exotic tidal disruption event (TDE). If the former is true, SDSS1335+0728 is one of the strongest cases of an AGNobserved in the process of activating. If the latter were found to be the case, it would correspond to the longest and faintest TDE ever observed (or another class of still unknown nuclear transient). Future observations of SDSS1335+0728 are crucial to further understand its behaviour. Key words. galaxies: active– accretion, accretion discs– galaxies: individual: SDSS J133519.91+072807.4
Discovery of An Apparent Red, High-Velocity Type Ia Supernova at 𝐳 = 2.9 wi...Sérgio Sacani
We present the JWST discovery of SN 2023adsy, a transient object located in a host galaxy JADES-GS
+
53.13485
−
27.82088
with a host spectroscopic redshift of
2.903
±
0.007
. The transient was identified in deep James Webb Space Telescope (JWST)/NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) program. Photometric and spectroscopic followup with NIRCam and NIRSpec, respectively, confirm the redshift and yield UV-NIR light-curve, NIR color, and spectroscopic information all consistent with a Type Ia classification. Despite its classification as a likely SN Ia, SN 2023adsy is both fairly red (
�
(
�
−
�
)
∼
0.9
) despite a host galaxy with low-extinction and has a high Ca II velocity (
19
,
000
±
2
,
000
km/s) compared to the general population of SNe Ia. While these characteristics are consistent with some Ca-rich SNe Ia, particularly SN 2016hnk, SN 2023adsy is intrinsically brighter than the low-
�
Ca-rich population. Although such an object is too red for any low-
�
cosmological sample, we apply a fiducial standardization approach to SN 2023adsy and find that the SN 2023adsy luminosity distance measurement is in excellent agreement (
≲
1
�
) with
Λ
CDM. Therefore unlike low-
�
Ca-rich SNe Ia, SN 2023adsy is standardizable and gives no indication that SN Ia standardized luminosities change significantly with redshift. A larger sample of distant SNe Ia is required to determine if SN Ia population characteristics at high-
�
truly diverge from their low-
�
counterparts, and to confirm that standardized luminosities nevertheless remain constant with redshift.
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Asymmetrical tidal tails of open star clusters: stars crossing their cluster’...Sérgio Sacani
The document discusses asymmetrical tidal tails observed around five open star clusters, which challenges Newtonian gravity. It summarizes how tidal tails form as stars escape clusters due to energy equipartition. Observations of the Hyades, Praesepe, Coma Berenices, COIN-Gaia 13, and NGC 752 clusters found more stars in the leading tidal tails within 50 pc of the clusters. Simulations show that in Newtonian gravity, tidal tails should be symmetrical, but asymmetries can arise in Milgromian dynamics. Future work is needed to better map tidal tails and develop Milgromian simulations.
The debris of the ‘last major merger’ is dynamically youngSérgio Sacani
The Milky Way’s (MW) inner stellar halo contains an [Fe/H]-rich component with highly eccentric orbits, often referred to as the
‘last major merger.’ Hypotheses for the origin of this component include Gaia-Sausage/Enceladus (GSE), where the progenitor
collided with the MW proto-disc 8–11 Gyr ago, and the Virgo Radial Merger (VRM), where the progenitor collided with the
MW disc within the last 3 Gyr. These two scenarios make different predictions about observable structure in local phase space,
because the morphology of debris depends on how long it has had to phase mix. The recently identified phase-space folds in Gaia
DR3 have positive caustic velocities, making them fundamentally different than the phase-mixed chevrons found in simulations
at late times. Roughly 20 per cent of the stars in the prograde local stellar halo are associated with the observed caustics. Based
on a simple phase-mixing model, the observed number of caustics are consistent with a merger that occurred 1–2 Gyr ago.
We also compare the observed phase-space distribution to FIRE-2 Latte simulations of GSE-like mergers, using a quantitative
measurement of phase mixing (2D causticality). The observed local phase-space distribution best matches the simulated data
1–2 Gyr after collision, and certainly not later than 3 Gyr. This is further evidence that the progenitor of the ‘last major merger’
did not collide with the MW proto-disc at early times, as is thought for the GSE, but instead collided with the MW disc within
the last few Gyr, consistent with the body of work surrounding the VRM.
Stellar-mass black holes in the Hyades star cluster?Sérgio Sacani
Astrophysical models of binary-black hole mergers in the Universe require a significant fraction of stellar-mass black holes (BHs)
to receive negligible natal kicks to explain the gravitational wave detections. This implies that BHs should be retained even in
open clusters with low escape velocities (≲ 1 km/s). We search for signatures of the presence of BHs in the nearest open cluster
to the Sun – the Hyades – by comparing density profiles of direct 𝑁-body models to data from Gaia. The observations are best
reproduced by models with 2−3 BHs at present. Models that never possessed BHs have an half-mass radius ∼ 30% smaller than
the observed value, while those where the last BHs were ejected recently (≲ 150 Myr ago) can still reproduce the density profile.
In 50% of the models hosting BHs, we find BHs with stellar companion(s). Their period distribution peaks at ∼ 103 yr, making
them unlikely to be found through velocity variations. We look for potential BH companions through large Gaia astrometric and
spectroscopic errors, identifying 56 binary candidates - none of which consistent with a massive compact companion. Models
with 2 − 3 BHs have an elevated central velocity dispersion, but observations can not yet discriminate. We conclude that the
present-day structure of the Hyades requires a significant fraction of BHs to receive natal kicks smaller than the escape velocity
of ∼ 3 km s−1
at the time of BH formation and that the nearest BHs to the Sun are in, or near, Hyades.
Collimation of the Relativistic Jet in the Quasar 3C273Sérgio Sacani
The collimation of relativistic jets launched from the vicinity of supermassive black holes (SMBHs) at the centers
of active galactic nuclei (AGNs) is one of the key questions to understand the nature of AGN jets. However, little is
known about the detailed jet structure for AGN like quasars since very high angular resolutions are required to
resolve these objects. We present very long baseline interferometry (VLBI) observations of the archetypical quasar
3C 273 at 86 GHz, performed with the Global Millimeter VLBI Array, for the first time including the Atacama
Large Millimeter/submillimeter Array. Our observations achieve a high angular resolution down to ∼60 μas,
resolving the innermost part of the jet ever on scales of ∼105 Schwarzschild radii. Our observations, including
close-in-time High Sensitivity Array observations of 3C 273 at 15, 22, and 43 GHz, suggest that the inner jet
collimates parabolically, while the outer jet expands conically, similar to jets from other nearby low-luminosity
AGNs. We discovered the jet collimation break around 107 Schwarzschild radii, providing the first compelling
evidence for structural transition in a quasar jet. The location of the collimation break for 3C 273 is farther
downstream from the sphere of gravitational influence (SGI) from the central SMBH. With the results for other
AGN jets, our results show that the end of the collimation zone in AGN jets is governed not only by the SGI of the
SMBH but also by the more diverse properties of the central nuclei.
Formation of low mass protostars and their circumstellar disksSérgio Sacani
Understanding circumstellar disks is of prime importance in astrophysics, however, their birth process remains poorly constrained due to observational and numerical challenges. Recent numerical works have shown that the small-scale physics, often wrapped into a sub-grid model, play a crucial role in disk formation and evolution. This calls for a combined approach in which both the protostar and circumstellar disk are studied in concert. Aims. We aim to elucidate the small scale physics and constrain sub-grid parameters commonly chosen in the literature by resolving the star-disk interaction. Methods. We carry out a set of very high resolution 3D radiative-hydrodynamics simulations that self-consistently describe the collapse of a turbulent dense molecular cloud core to stellar densities. We study the birth of the protostar, the circumstellar disk, and its early evolution (< 6 yr after protostellar formation). Results. Following the second gravitational collapse, the nascent protostar quickly reaches breakup velocity and sheds its surface material, thus forming a hot (∼ 103 K), dense, and highly flared circumstellar disk. The protostar is embedded within the disk, such that material can flow without crossing any shock fronts. The circumstellar disk mass quickly exceeds that of the protostar, and its kinematics are dominated by self-gravity. Accretion onto the disk is highly anisotropic, and accretion onto the protostar mainly occurs through material that slides on the disk surface. The polar mass flux is negligible in comparison. The radiative behavior also displays a strong anisotropy, as the polar accretion shock is shown to be supercritical whereas its equatorial counterpart is subcritical. We also f ind a remarkable convergence of our results with respect to initial conditions. Conclusions. These results reveal the structure and kinematics in the smallest spatial scales relevant to protostellar and circumstellar disk evolution. They can be used to describe accretion onto regions commonly described by sub-grid models in simulations studying larger scale physics.
Detection of anisotropic satellite quenching in galaxy clusters up to z ∼ 1Sérgio Sacani
Satellite galaxies in the cluster environment are more likely to be quenched than galaxies in the general field. Recently, it has
been reported that satellite galaxy quenching depends on the orientation relative to their central galaxies: satellites along the
major axis of centrals are more likely to be quenched than those along the minor axis. In this paper, we report a detection
of such anisotropic quenching up to z ∼ 1 based on a large optically selected cluster catalogue constructed from the Hyper
Suprime-Cam Subaru Strategic Program. We calculate the quiescent satellite galaxy fraction as a function of orientation angle
measured from the major axis of central galaxies and find that the quiescent fractions at 0.25 < z < 1 are reasonably fitted
by sinusoidal functions with amplitudes of a few per cent. Anisotropy is clearer in inner regions (<r200m) of clusters and not
significant in cluster outskirts (>r200m). We also confirm that the observed anisotropy cannot be explained by differences in
local galaxy density or stellar mass distribution along the two axes. Quiescent fraction excesses between the two axes suggest
that the quenching efficiency contributing to the anisotropy is almost independent of stellar mass, at least down to our stellar
mass limit of M∗ = 1 × 1010 M. Finally, we argue that the physical origins of the observed anisotropy should have shorter
quenching time-scales than ∼ 1 Gyr, like ram-pressure stripping, because, for anisotropic quenching to be observed, satellites
must be quenched before their initial orientation angles are significantly changed.
Kinematics and simulations_of_the_stellar_stream_in_the_halo_of_the_umbrella_...Sérgio Sacani
This document summarizes a study of the stellar stream and substructures around the Umbrella Galaxy (NGC 4651). Deep imaging and spectroscopy were used to characterize the properties and kinematics of the stream. Tracer objects like globular clusters and planetary nebulae were identified and found to delineate a kinematically cold feature in position-velocity space. Dynamical modeling suggests the stream originated from the tidal disruption of a dwarf galaxy on a highly eccentric orbit about 6-10 billion years ago. This work demonstrates the feasibility of using discrete tracers to recover the kinematics and model the dynamics of low surface brightness stellar streams around distant galaxies.
Galaxy interactions are the dominant trigger for local type 2 quasarsSérgio Sacani
The triggering mechanism for the most luminous, quasar-like active galactic nuclei (AGN) remains a source of debate, with
some studies favouring triggering via galaxy mergers, but others finding little evidence to support this mechanism. Here, we
present deep Isaac Newton Telescope/Wide Field Camera imaging observations of a complete sample of 48 optically selected
type 2 quasars – the QSOFEED sample (L[O III] > 108.5 L; z < 0.14). Based on visual inspection by eight classifiers, we find
clear evidence that galaxy interactions are the dominant triggering mechanism for quasar activity in the local universe, with
65+6
−7 per cent of the type 2 quasar hosts showing morphological features consistent with galaxy mergers or encounters, compared
with only 22+5
−4 per cent of a stellar-mass- and redshift-matched comparison sample of non-AGN galaxies – a 5σ difference. The
type 2 quasar hosts are a factor of 3.0+0.5 −0.8 more likely to be morphologically disturbed than their matched non-AGN counterparts,
similar to our previous results for powerful 3CR radio AGN of comparable [O III] emission-line luminosity and redshift. In
contrast to the idea that quasars are triggered at the peaks of galaxy mergers as the two nuclei coalesce, and only become
visible post-coalescence, the majority of morphologically disturbed type 2 quasar sources in our sample are observed in the
pre-coalescence phase (61+8
−9 per cent). We argue that much of the apparent ambiguity that surrounds observational results in this
field is a result of differences in the surface brightness depths of the observations, combined with the effects of cosmological
surface brightness dimming.
The Expansion of the X-Ray Nebula Around η CarSérgio Sacani
1. The author analyzes over 20 years of Chandra X-ray images to measure for the first time the expansion of the X-ray nebula around η Carinae.
2. A combined Chandra image reveals a faint, nearly uniform elliptical shell surrounding the X-ray bright ring, with a similar orientation and shape as the Homunculus nebula but about 3 times larger.
3. The author measures proper motions of brighter regions associated with the X-ray emitting ring, such as the S-ridge and W-arc. Motions are consistent with optical studies of ejecta from the 1840s Great Eruption.
We present the 2020 version of the Siena Galaxy Atlas (SGA-2020), a multiwavelength optical and infrared
imaging atlas of 383,620 nearby galaxies. The SGA-2020 uses optical grz imaging over ≈20,000 deg2 from the
Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys Data Release 9 and infrared imaging in
four bands (spanning 3.4–22 μm) from the 6 year unWISE coadds; it is more than 95% complete for galaxies larger
than R(26) ≈ 25″ and r < 18 measured at the 26 mag arcsec−2 isophote in the r band. The atlas delivers precise
coordinates, multiwavelength mosaics, azimuthally averaged optical surface-brightness profiles, model images and
photometry, and additional ancillary metadata for the full sample. Coupled with existing and forthcoming optical
spectroscopy from the DESI, the SGA-2020 will facilitate new detailed studies of the star formation and mass
assembly histories of nearby galaxies; enable precise measurements of the local velocity field via the Tully–Fisher
and fundamental plane relations; serve as a reference sample of lasting legacy value for time-domain and
multimessenger astronomical events; and more.
A giant thin stellar stream in the Coma Galaxy ClusterSérgio Sacani
The study of dynamically cold stellar streams reveals information about the gravitational potential where they reside and provides
important constraints on the properties of dark matter. However, the intrinsic faintness of these streams makes their detection beyond
Local environments highly challenging. Here, we report the detection of an extremely faint stellar stream (µg,max = 29.5 mag arcsec−2
)
with an extraordinarily coherent and thin morphology in the Coma Galaxy Cluster. This Giant Coma Stream spans ∼510 kpc in length
and appears as a free-floating structure located at a projected distance of 0.8 Mpc from the center of Coma. We do not identify any
potential galaxy remnant or core, and the stream structure appears featureless in our data. We interpret the Giant Coma Stream as
being a recently accreted, tidally disrupting passive dwarf. Using the Illustris-TNG50 simulation, we identify a case with similar
characteristics, showing that, although rare, these types of streams are predicted to exist in Λ-CDM. Our work unveils the presence
of free-floating, extremely faint and thin stellar streams in galaxy clusters, widening the environmental context in which these objects
are found ahead of their promising future application in the study of the properties of dark matter.
AT2023fhn (the Finch): a Luminous Fast Blue Optical Transient at a large offs...Sérgio Sacani
Luminous Fast Blue Optical Transients (LFBOTs) - the prototypical example being AT 2018cow - are a rare class of events
whose origins are poorly understood. They are characterised by rapid evolution, featureless blue spectra at early times, and
luminous X-ray and radio emission. LFBOTs thus far have been found exclusively at small projected offsets from star-forming
host galaxies. We present Hubble Space Telescope, Gemini, Chandra and Very Large Array observations of a new LFBOT,
AT 2023fhn. The Hubble Space Telescope data reveal a large offset (> 3.5 half-light radii) from the two closest galaxies, both
at redshift 𝑧 ∼ 0.24. The location of AT 2023fhn is in stark contrast with previous events, and demonstrates that LFBOTs can
occur in a range of galactic environments.
Triple Spiral Arms of a Triple Protostar System Imaged in Molecular LinesSérgio Sacani
Most stars form in multiple-star systems. For a better understanding of their formation processes, it is important to
resolve the individual protostellar components and the surrounding envelope and disk material at the earliest
possible formation epoch, because the formation history can be lost in a few orbital timescales. Here we present
Atacama Large Millimeter/submillimeter Array observational results of a young multiple protostellar system,
IRAS 04239+2436, where three well-developed large spiral arms were detected in the shocked SO emission.
Along the most conspicuous arm, the accretion streamer was also detected in the SO2 emission. The observational
results are complemented by numerical magnetohydrodynamic simulations, where those large arms only appear in
magnetically weakened clouds. Numerical simulations also suggest that the large triple spiral arms are the result of
gravitational interactions between compact triple protostars and the turbulent infalling envelope.
The galaxy morphology–density relation in the EAGLE simulationSérgio Sacani
This study uses a convolutional neural network trained on observed galaxy images to classify galaxies in the EAGLE cosmological hydrodynamical simulation by visual morphology. It finds that EAGLE reproduces both the observed relationships between galaxy morphology and local density (the morphology-density relation), and between morphology and galaxy mass. Through analysis of the simulations, the key processes identified as driving the morphology-density relation are: (1) the transformation of disc galaxies into lenticular galaxies via gas stripping in dense environments, (2) the formation of lenticular galaxies through merger-induced black hole feedback in less dense environments, and (3) the increasing fraction of more elliptical, high-mass galaxies at higher densities.
How to tell an accreting boson star from a black hole h. olivares et al (2020)SOCIEDAD JULIO GARAVITO
Abstract
The tentative evidences for late time “echoes” in LIGO gravitational
waves (GWs) have been claimed to be signatures of horizonless compact
objects rather than vacuum black holes (BHs) possessing horizons. In
general, in the past, many authors have considered the possibility that
the so-called BHs might be only BH mimickers (BHMs). And recently
it has been suggested that the true astrophysical BH having no intrinsic
magnetic fields may be differentiated from magnetized BHMs by studying
the radial variations of magnetic fields around pertinent compact objects
(Lobanov, Nat. Astron. 2017). Here we highlight that close to the surface
of BHMs, the magnetic field pattern differs significantly from the same for
non-relativistic Neutron Stars (B ∼ r −3 ). In particular, we point out that
for ultra- compact BHMs, the polar field is weaker than the equatorial field
1by an extremely large factor of ∼ z s /lnz s , where z s ≫ 1 is the surface
gravitational redshift. We suggest that by studying the of radial variation
as well as such significant asymmetry of magnetic field structure near the
compact object, future observations may differentiate a theoretical black
hole from a astrophysical BH mimicker (a compact object). This study
also shows that even if some BHMs would be hypothesized to possess
magnetic fields even stronger than that of magnetars, in certain cases, they
may effectively behave as atoll type neutron stars possessing extremely low
magnetic fields.
Keywords: X-ray Binaries; Active Galactic Nuclei; Magnetic Field;
Black Hole Mimickers; Relativistic Astrophysics.
PACS numbers: 04.40.Dg, 97.80.Jp, 97.60.Gb, 95.86.Nv.
Dust Enrichment and Grain Growth in a Smooth Disk around the DG Tau Protostar...Sérgio Sacani
Characterizing the physical properties of dust grains in a protoplanetary disk is critical to comprehending the planet
formation process. Our study presents Atacama Large Millimeter/submillimeter Array (ALMA) high-resolution
observations of the young protoplanetary disk around DG Tau at a 1.3 mm dust continuum. The observations, with
a spatial resolution of ≈0 04, or ≈5 au, revealed a geometrically thin and smooth disk without substantial
substructures, suggesting that the disk retains the initial conditions of the planet formation. To further analyze the
distributions of dust surface density, temperature, and grain size, we conducted a multiband analysis with several
dust models, incorporating ALMA archival data of the 0.87 and 3.1 mm dust polarization. The results showed that
the Toomre Q parameter is 2 at a 20 au radius, assuming a dust-to-gas mass ratio of 0.01. This implies that a
higher dust-to-gas mass ratio is necessary to stabilize the disk. The grain sizes depend on the dust models, and for
the DSHARP compact dust, they were found to be smaller than ∼400 μm in the inner region (r 20 au) while
exceeding larger than 3 mm in the outer part. Radiative transfer calculations show that the dust scale height is lower
than at least one-third of the gas scale height. These distributions of dust enrichment, grain sizes, and weak
turbulence strength may have significant implications for the formation of planetesimals through mechanisms such
as streaming instability. We also discuss the CO snowline effect and collisional fragmentation in dust coagulation
for the origin of the dust size distribution.
The SAMI Galaxy Sur v ey: galaxy spin is more strongly correlated with stella...Sérgio Sacani
We use the SAMI Galaxy Surv e y to examine the drivers of galaxy spin, λR e , in a multidimensional parameter space including stellar mass, stellar population age (or specific star formation rate), and various environmental metrics (local density, halo mass, satellite versus central). Using a partial correlation analysis, we consistently find that age or specific star formation rate is the primary parameter correlating with spin. Light-weighted age and specific star formation rate are more strongly correlated with spin than mass-weighted age. In fact, across our sample, once the relation between light-weighted age and spin is accounted for, there is no significant residual correlation between spin and mass, or spin and environment. This result is strongly suggestive that the present-day environment only indirectly influences spin, via the removal of gas and star formation quenching. That is, environment affects age, then age affects spin. Older galaxies then have lower spin, either due to stars being born dynamically hotter at high redshift, or due to secular heating. Our results appear to rule out environmentally dependent dynamical heating (e.g. g alaxy–g alaxy interactions) being important, at least within 1 R e where our kinematic measurements are made. The picture is more complex when we only consider high-mass galaxies ( M ∗ ≳ 10 11 M ). While the age-spin relation is still strong for these high-mass galaxies, there is a residual environmental trend with central galaxies preferentially having lower spin, compared to satellites of the same age and mass. We argue that this trend is likely due to central galaxies being a preferred location for mergers.
Betelgeuse as a Merger of a Massive Star with a CompanionSérgio Sacani
This document summarizes a study that uses 3D hydrodynamic simulations and 1D stellar evolution modeling to investigate the merger of a 16 solar mass star with a 4 solar mass companion star. The simulations show the companion spirals inward and merges with the primary star's helium core. Approximately 0.6 solar masses of material is ejected in an asymmetric, bipolar outflow. The post-merger structure is then modeled in 1D stellar evolution, showing in some cases the star evolves to have surface properties similar to Betelgeus, with rapid rotation and enhanced nitrogen at the surface. This pioneering study aims to comprehensively model stellar mergers across dynamical, thermal, and nuclear evolutionary timescales.
Candidate young stellar objects in the S-cluster: Kinematic analysis of a sub...Sérgio Sacani
Context. The observation of several L-band emission sources in the S cluster has led to a rich discussion of their nature. However, a definitive answer to the classification of the dusty objects requires an explanation for the detection of compact Doppler-shifted Brγ emission. The ionized hydrogen in combination with the observation of mid-infrared L-band continuum emission suggests that most of these sources are embedded in a dusty envelope. These embedded sources are part of the S-cluster, and their relationship to the S-stars is still under debate. To date, the question of the origin of these two populations has been vague, although all explanations favor migration processes for the individual cluster members. Aims. This work revisits the S-cluster and its dusty members orbiting the supermassive black hole SgrA* on bound Keplerian orbits from a kinematic perspective. The aim is to explore the Keplerian parameters for patterns that might imply a nonrandom distribution of the sample. Additionally, various analytical aspects are considered to address the nature of the dusty sources. Methods. Based on the photometric analysis, we estimated the individual H−K and K−L colors for the source sample and compared the results to known cluster members. The classification revealed a noticeable contrast between the S-stars and the dusty sources. To fit the flux-density distribution, we utilized the radiative transfer code HYPERION and implemented a young stellar object Class I model. We obtained the position angle from the Keplerian fit results; additionally, we analyzed the distribution of the inclinations and the longitudes of the ascending node. Results. The colors of the dusty sources suggest a stellar nature consistent with the spectral energy distribution in the near and midinfrared domains. Furthermore, the evaporation timescales of dusty and gaseous clumps in the vicinity of SgrA* are much shorter ( 2yr) than the epochs covered by the observations (≈15yr). In addition to the strong evidence for the stellar classification of the D-sources, we also find a clear disk-like pattern following the arrangements of S-stars proposed in the literature. Furthermore, we find a global intrinsic inclination for all dusty sources of 60 ± 20◦, implying a common formation process. Conclusions. The pattern of the dusty sources manifested in the distribution of the position angles, inclinations, and longitudes of the ascending node strongly suggests two different scenarios: the main-sequence stars and the dusty stellar S-cluster sources share a common formation history or migrated with a similar formation channel in the vicinity of SgrA*. Alternatively, the gravitational influence of SgrA* in combination with a massive perturber, such as a putative intermediate mass black hole in the IRS 13 cluster, forces the dusty objects and S-stars to follow a particular orbital arrangement. Key words. stars: black holes– stars: formation– Galaxy: center– galaxies: star formation
Ähnlich wie Detecting a disc bending wave in a barred-spiral galaxy at redshift 4.4 (20)
SDSS1335+0728: The awakening of a ∼ 106M⊙ black hole⋆Sérgio Sacani
Context. The early-type galaxy SDSS J133519.91+072807.4 (hereafter SDSS1335+0728), which had exhibited no prior optical variations during the preceding two decades, began showing significant nuclear variability in the Zwicky Transient Facility (ZTF) alert stream from December 2019 (as ZTF19acnskyy). This variability behaviour, coupled with the host-galaxy properties, suggests that SDSS1335+0728 hosts a ∼ 106M⊙ black hole (BH) that is currently in the process of ‘turning on’. Aims. We present a multi-wavelength photometric analysis and spectroscopic follow-up performed with the aim of better understanding the origin of the nuclear variations detected in SDSS1335+0728. Methods. We used archival photometry (from WISE, 2MASS, SDSS, GALEX, eROSITA) and spectroscopic data (from SDSS and LAMOST) to study the state of SDSS1335+0728 prior to December 2019, and new observations from Swift, SOAR/Goodman, VLT/X-shooter, and Keck/LRIS taken after its turn-on to characterise its current state. We analysed the variability of SDSS1335+0728 in the X-ray/UV/optical/mid-infrared range, modelled its spectral energy distribution prior to and after December 2019, and studied the evolution of its UV/optical spectra. Results. From our multi-wavelength photometric analysis, we find that: (a) since 2021, the UV flux (from Swift/UVOT observations) is four times brighter than the flux reported by GALEX in 2004; (b) since June 2022, the mid-infrared flux has risen more than two times, and the W1−W2 WISE colour has become redder; and (c) since February 2024, the source has begun showing X-ray emission. From our spectroscopic follow-up, we see that (i) the narrow emission line ratios are now consistent with a more energetic ionising continuum; (ii) broad emission lines are not detected; and (iii) the [OIII] line increased its flux ∼ 3.6 years after the first ZTF alert, which implies a relatively compact narrow-line-emitting region. Conclusions. We conclude that the variations observed in SDSS1335+0728 could be either explained by a ∼ 106M⊙ AGN that is just turning on or by an exotic tidal disruption event (TDE). If the former is true, SDSS1335+0728 is one of the strongest cases of an AGNobserved in the process of activating. If the latter were found to be the case, it would correspond to the longest and faintest TDE ever observed (or another class of still unknown nuclear transient). Future observations of SDSS1335+0728 are crucial to further understand its behaviour. Key words. galaxies: active– accretion, accretion discs– galaxies: individual: SDSS J133519.91+072807.4
Discovery of An Apparent Red, High-Velocity Type Ia Supernova at 𝐳 = 2.9 wi...Sérgio Sacani
We present the JWST discovery of SN 2023adsy, a transient object located in a host galaxy JADES-GS
+
53.13485
−
27.82088
with a host spectroscopic redshift of
2.903
±
0.007
. The transient was identified in deep James Webb Space Telescope (JWST)/NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) program. Photometric and spectroscopic followup with NIRCam and NIRSpec, respectively, confirm the redshift and yield UV-NIR light-curve, NIR color, and spectroscopic information all consistent with a Type Ia classification. Despite its classification as a likely SN Ia, SN 2023adsy is both fairly red (
�
(
�
−
�
)
∼
0.9
) despite a host galaxy with low-extinction and has a high Ca II velocity (
19
,
000
±
2
,
000
km/s) compared to the general population of SNe Ia. While these characteristics are consistent with some Ca-rich SNe Ia, particularly SN 2016hnk, SN 2023adsy is intrinsically brighter than the low-
�
Ca-rich population. Although such an object is too red for any low-
�
cosmological sample, we apply a fiducial standardization approach to SN 2023adsy and find that the SN 2023adsy luminosity distance measurement is in excellent agreement (
≲
1
�
) with
Λ
CDM. Therefore unlike low-
�
Ca-rich SNe Ia, SN 2023adsy is standardizable and gives no indication that SN Ia standardized luminosities change significantly with redshift. A larger sample of distant SNe Ia is required to determine if SN Ia population characteristics at high-
�
truly diverge from their low-
�
counterparts, and to confirm that standardized luminosities nevertheless remain constant with redshift.
Evidence of Jet Activity from the Secondary Black Hole in the OJ 287 Binary S...Sérgio Sacani
Wereport the study of a huge optical intraday flare on 2021 November 12 at 2 a.m. UT in the blazar OJ287. In the binary black hole model, it is associated with an impact of the secondary black hole on the accretion disk of the primary. Our multifrequency observing campaign was set up to search for such a signature of the impact based on a prediction made 8 yr earlier. The first I-band results of the flare have already been reported by Kishore et al. (2024). Here we combine these data with our monitoring in the R-band. There is a big change in the R–I spectral index by 1.0 ±0.1 between the normal background and the flare, suggesting a new component of radiation. The polarization variation during the rise of the flare suggests the same. The limits on the source size place it most reasonably in the jet of the secondary BH. We then ask why we have not seen this phenomenon before. We show that OJ287 was never before observed with sufficient sensitivity on the night when the flare should have happened according to the binary model. We also study the probability that this flare is just an oversized example of intraday variability using the Krakow data set of intense monitoring between 2015 and 2023. We find that the occurrence of a flare of this size and rapidity is unlikely. In machine-readable Tables 1 and 2, we give the full orbit-linked historical light curve of OJ287 as well as the dense monitoring sample of Krakow.
JAMES WEBB STUDY THE MASSIVE BLACK HOLE SEEDSSérgio Sacani
The pathway(s) to seeding the massive black holes (MBHs) that exist at the heart of galaxies in the present and distant Universe remains an unsolved problem. Here we categorise, describe and quantitatively discuss the formation pathways of both light and heavy seeds. We emphasise that the most recent computational models suggest that rather than a bimodal-like mass spectrum between light and heavy seeds with light at one end and heavy at the other that instead a continuum exists. Light seeds being more ubiquitous and the heavier seeds becoming less and less abundant due the rarer environmental conditions required for their formation. We therefore examine the different mechanisms that give rise to different seed mass spectrums. We show how and why the mechanisms that produce the heaviest seeds are also among the rarest events in the Universe and are hence extremely unlikely to be the seeds for the vast majority of the MBH population. We quantify, within the limits of the current large uncertainties in the seeding processes, the expected number densities of the seed mass spectrum. We argue that light seeds must be at least 103 to 105 times more numerous than heavy seeds to explain the MBH population as a whole. Based on our current understanding of the seed population this makes heavy seeds (Mseed > 103 M⊙) a significantly more likely pathway given that heavy seeds have an abundance pattern than is close to and likely in excess of 10−4 compared to light seeds. Finally, we examine the current state-of-the-art in numerical calculations and recent observations and plot a path forward for near-future advances in both domains.
Anti-Universe And Emergent Gravity and the Dark UniverseSérgio Sacani
Recent theoretical progress indicates that spacetime and gravity emerge together from the entanglement structure of an underlying microscopic theory. These ideas are best understood in Anti-de Sitter space, where they rely on the area law for entanglement entropy. The extension to de Sitter space requires taking into account the entropy and temperature associated with the cosmological horizon. Using insights from string theory, black hole physics and quantum information theory we argue that the positive dark energy leads to a thermal volume law contribution to the entropy that overtakes the area law precisely at the cosmological horizon. Due to the competition between area and volume law entanglement the microscopic de Sitter states do not thermalise at sub-Hubble scales: they exhibit memory effects in the form of an entropy displacement caused by matter. The emergent laws of gravity contain an additional ‘dark’ gravitational force describing the ‘elastic’ response due to the entropy displacement. We derive an estimate of the strength of this extra force in terms of the baryonic mass, Newton’s constant and the Hubble acceleration scale a0 = cH0, and provide evidence for the fact that this additional ‘dark gravity force’ explains the observed phenomena in galaxies and clusters currently attributed to dark matter.
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Sérgio Sacani
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the
atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets
receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric
composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet
transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (Porb) of 12.76 days.
The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous Porb from TESS data. We
confirmed the transit signal and Porb using ground-based photometry with MuSCAT2 and MuSCAT3, and
validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as
well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope
and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host
star is inactive, with an X-ray-to-bolometric luminosity ratio of log 5.7 L L X bol » - . Joint analysis of the light
curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R⊕,a3σ mass upper limit of
3.9 M⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric
(TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small
list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TES...Sérgio Sacani
We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a
bright (V = 12.6 mag, K = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the
lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors
42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations
with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory,
as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of
12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent
future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar
compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool
stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy.
The importance of continents, oceans and plate tectonics for the evolution of...Sérgio Sacani
Within the uncertainties of involved astronomical and biological parameters, the Drake Equation
typically predicts that there should be many exoplanets in our galaxy hosting active, communicative
civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is
often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing
the importance of planetary tectonic style for biological evolution. We summarize growing evidence
that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern
plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated
emergence and evolution of complex species. We further suggest that both continents and oceans
are required for ACCs because early evolution of simple life must happen in water but late evolution
of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox
(1) by adding two additional terms to the Drake Equation: foc
(the fraction of habitable exoplanets
with significant continents and oceans) and fpt
(the fraction of habitable exoplanets with significant
continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by
demonstrating that the product of foc
and fpt
is very small (< 0.00003–0.002). We propose that the lack
of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on
exoplanets with primitive life.
A Giant Impact Origin for the First Subduction on EarthSérgio Sacani
Hadean zircons provide a potential record of Earth's earliest subduction 4.3 billion years ago. Itremains enigmatic how subduction could be initiated so soon after the presumably Moon‐forming giant impact(MGI). Earlier studies found an increase in Earth's core‐mantle boundary (CMB) temperature due to theaccumulation of the impactor's core, and our recent work shows Earth's lower mantle remains largely solid, withsome of the impactor's mantle potentially surviving as the large low‐shear velocity provinces (LLSVPs). Here,we show that a hot post‐impact CMB drives the initiation of strong mantle plumes that can induce subductioninitiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMBtemperature is the primary factor triggering early subduction, with enrichment of heat‐producing elements inLLSVPs as another potential factor. The models link the earliest subduction to the MGI with implications forunderstanding the diverse tectonic regimes of rocky planets.
Climate extremes likely to drive land mammal extinction during next supercont...Sérgio Sacani
Mammals have dominated Earth for approximately 55 Myr thanks to their
adaptations and resilience to warming and cooling during the Cenozoic. All
life will eventually perish in a runaway greenhouse once absorbed solar
radiation exceeds the emission of thermal radiation in several billions of
years. However, conditions rendering the Earth naturally inhospitable to
mammals may develop sooner because of long-term processes linked to
plate tectonics (short-term perturbations are not considered here). In
~250 Myr, all continents will converge to form Earth’s next supercontinent,
Pangea Ultima. A natural consequence of the creation and decay of Pangea
Ultima will be extremes in pCO2 due to changes in volcanic rifting and
outgassing. Here we show that increased pCO2, solar energy (F⨀;
approximately +2.5% W m−2 greater than today) and continentality (larger
range in temperatures away from the ocean) lead to increasing warming
hostile to mammalian life. We assess their impact on mammalian
physiological limits (dry bulb, wet bulb and Humidex heat stress indicators)
as well as a planetary habitability index. Given mammals’ continued survival,
predicted background pCO2 levels of 410–816 ppm combined with increased
F⨀ will probably lead to a climate tipping point and their mass extinction.
The results also highlight how global landmass configuration, pCO2 and F⨀
play a critical role in planetary habitability.
Constraints on Neutrino Natal Kicks from Black-Hole Binary VFTS 243Sérgio Sacani
The recently reported observation of VFTS 243 is the first example of a massive black-hole binary
system with negligible binary interaction following black-hole formation. The black-hole mass (≈10M⊙)
and near-circular orbit (e ≈ 0.02) of VFTS 243 suggest that the progenitor star experienced complete
collapse, with energy-momentum being lost predominantly through neutrinos. VFTS 243 enables us to
constrain the natal kick and neutrino-emission asymmetry during black-hole formation. At 68% confidence
level, the natal kick velocity (mass decrement) is ≲10 km=s (≲1.0M⊙), with a full probability distribution
that peaks when ≈0.3M⊙ were ejected, presumably in neutrinos, and the black hole experienced a natal
kick of 4 km=s. The neutrino-emission asymmetry is ≲4%, with best fit values of ∼0–0.2%. Such a small
neutrino natal kick accompanying black-hole formation is in agreement with theoretical predictions.
Detectability of Solar Panels as a TechnosignatureSérgio Sacani
In this work, we assess the potential detectability of solar panels made of silicon on an Earth-like
exoplanet as a potential technosignature. Silicon-based photovoltaic cells have high reflectance in the
UV-VIS and in the near-IR, within the wavelength range of a space-based flagship mission concept
like the Habitable Worlds Observatory (HWO). Assuming that only solar energy is used to provide
the 2022 human energy needs with a land cover of ∼ 2.4%, and projecting the future energy demand
assuming various growth-rate scenarios, we assess the detectability with an 8 m HWO-like telescope.
Assuming the most favorable viewing orientation, and focusing on the strong absorption edge in the
ultraviolet-to-visible (0.34 − 0.52 µm), we find that several 100s of hours of observation time is needed
to reach a SNR of 5 for an Earth-like planet around a Sun-like star at 10pc, even with a solar panel
coverage of ∼ 23% land coverage of a future Earth. We discuss the necessity of concepts like Kardeshev
Type I/II civilizations and Dyson spheres, which would aim to harness vast amounts of energy. Even
with much larger populations than today, the total energy use of human civilization would be orders of
magnitude below the threshold for causing direct thermal heating or reaching the scale of a Kardashev
Type I civilization. Any extraterrrestrial civilization that likewise achieves sustainable population
levels may also find a limit on its need to expand, which suggests that a galaxy-spanning civilization
as imagined in the Fermi paradox may not exist.
Jet reorientation in central galaxies of clusters and groups: insights from V...Sérgio Sacani
Recent observations of galaxy clusters and groups with misalignments between their central AGN jets
and X-ray cavities, or with multiple misaligned cavities, have raised concerns about the jet – bubble
connection in cooling cores, and the processes responsible for jet realignment. To investigate the
frequency and causes of such misalignments, we construct a sample of 16 cool core galaxy clusters and
groups. Using VLBA radio data we measure the parsec-scale position angle of the jets, and compare
it with the position angle of the X-ray cavities detected in Chandra data. Using the overall sample
and selected subsets, we consistently find that there is a 30% – 38% chance to find a misalignment
larger than ∆Ψ = 45◦ when observing a cluster/group with a detected jet and at least one cavity. We
determine that projection may account for an apparently large ∆Ψ only in a fraction of objects (∼35%),
and given that gas dynamical disturbances (as sloshing) are found in both aligned and misaligned
systems, we exclude environmental perturbation as the main driver of cavity – jet misalignment.
Moreover, we find that large misalignments (up to ∼ 90◦
) are favored over smaller ones (45◦ ≤ ∆Ψ ≤
70◦
), and that the change in jet direction can occur on timescales between one and a few tens of Myr.
We conclude that misalignments are more likely related to actual reorientation of the jet axis, and we
discuss several engine-based mechanisms that may cause these dramatic changes.
The solar dynamo begins near the surfaceSérgio Sacani
The magnetic dynamo cycle of the Sun features a distinct pattern: a propagating
region of sunspot emergence appears around 30° latitude and vanishes near the
equator every 11 years (ref. 1). Moreover, longitudinal flows called torsional oscillations
closely shadow sunspot migration, undoubtedly sharing a common cause2. Contrary
to theories suggesting deep origins of these phenomena, helioseismology pinpoints
low-latitude torsional oscillations to the outer 5–10% of the Sun, the near-surface
shear layer3,4. Within this zone, inwardly increasing differential rotation coupled with
a poloidal magnetic field strongly implicates the magneto-rotational instability5,6,
prominent in accretion-disk theory and observed in laboratory experiments7.
Together, these two facts prompt the general question: whether the solar dynamo is
possibly a near-surface instability. Here we report strong affirmative evidence in stark
contrast to traditional models8 focusing on the deeper tachocline. Simple analytic
estimates show that the near-surface magneto-rotational instability better explains
the spatiotemporal scales of the torsional oscillations and inferred subsurface
magnetic field amplitudes9. State-of-the-art numerical simulations corroborate these
estimates and reproduce hemispherical magnetic current helicity laws10. The dynamo
resulting from a well-understood near-surface phenomenon improves prospects
for accurate predictions of full magnetic cycles and space weather, affecting the
electromagnetic infrastructure of Earth.
Travis Hills of MN is Making Clean Water Accessible to All Through High Flux ...Travis Hills MN
By harnessing the power of High Flux Vacuum Membrane Distillation, Travis Hills from MN envisions a future where clean and safe drinking water is accessible to all, regardless of geographical location or economic status.
PPT on Direct Seeded Rice presented at the three-day 'Training and Validation Workshop on Modules of Climate Smart Agriculture (CSA) Technologies in South Asia' workshop on April 22, 2024.
Sexuality - Issues, Attitude and Behaviour - Applied Social Psychology - Psyc...PsychoTech Services
A proprietary approach developed by bringing together the best of learning theories from Psychology, design principles from the world of visualization, and pedagogical methods from over a decade of training experience, that enables you to: Learn better, faster!
When I was asked to give a companion lecture in support of ‘The Philosophy of Science’ (https://shorturl.at/4pUXz) I decided not to walk through the detail of the many methodologies in order of use. Instead, I chose to employ a long standing, and ongoing, scientific development as an exemplar. And so, I chose the ever evolving story of Thermodynamics as a scientific investigation at its best.
Conducted over a period of >200 years, Thermodynamics R&D, and application, benefitted from the highest levels of professionalism, collaboration, and technical thoroughness. New layers of application, methodology, and practice were made possible by the progressive advance of technology. In turn, this has seen measurement and modelling accuracy continually improved at a micro and macro level.
Perhaps most importantly, Thermodynamics rapidly became a primary tool in the advance of applied science/engineering/technology, spanning micro-tech, to aerospace and cosmology. I can think of no better a story to illustrate the breadth of scientific methodologies and applications at their best.
(June 12, 2024) Webinar: Development of PET theranostics targeting the molecu...Scintica Instrumentation
Targeting Hsp90 and its pathogen Orthologs with Tethered Inhibitors as a Diagnostic and Therapeutic Strategy for cancer and infectious diseases with Dr. Timothy Haystead.
2. 8942 T. Tsukui et al.
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some simulations suggest molecular gas can suppress bar formation
or result in a weaker bar (Athanassoula, Machado Rodionov 2013;
Łokas 2020). Conversely, ALMA observations reveal prevalent bar
morphologies in dust continuum images of gas-rich submillimeter
galaxies (Gullberg et al. 2019; Hodge et al. 2019; Smail et al.
2023). Tidal interaction is another promising avenue to form bars
(e.g. Noguchi 1996; Łokas et al. 2014, 2016), even for gas-rich
systems (Gajda, Łokas Athanassoula 2018). Recent cosmological
simulations, including a realistic high gas fraction of high-redshift
galaxies and external effects such as mergers, suggest a high bar
fraction out to z ∼ 4 (Rosas-Guevara et al. 2022). Different sub-grid
physics implementations in simulations can result in different galaxy
properties and bar dynamics (Fragkoudi et al. 2021).
Recently, Tsukui Iguchi 2021 revealed a spiral morphology
in BRI 1335–0417 at z = 4.4074 (Guilloteau et al. 1997), hosting
an optical quasar initially identified in Automatic Plate Measuring
(APM) survey (Storrie-Lombardi et al. 1996). The galaxy exhibits a
high star formation rate (SFR) ∼1700 M yr−1
estimated from the
spectral energy distribution modelling with the AGN contribution
being corrected using spatially resolved information (point source
and extended source separation; Tsukui et al. 2023b), making it one
of the brightest unlensed submillimeter source at z 4 (Jones et al.
2016). The [C II] and dust continuum maps of the galaxy revealed a
two-armed structure with a pitch angle of 26.7+4.1
−1.6
◦
(Tsukui Iguchi
2021). These arms extend from 2 to 5 kpc and appear to start at the
end of an elongated bar-like structure that bridges them.
Despite new observational and theoretical results, it remains
unclear what was the dominant cause for early bar and spiral
formation – internal or external processes. As the brightest and
earliest barred spiral example, BRI 1335–0417 allows us to study the
detailed [C II] line and FIR continuum morphology in unprecedented
detail and without uncertainties due to lens model reconstruction.
The spatially resolved [C II] line kinematics together with numerical
simulations provide an excellent laboratory to provide new insights
into early bar formation.
Gas disc kinematics tell us not only the dynamics of the galaxy,
such as disc stability and underlying mass distribution of the galaxy.
Subtracting the overall rotation and examining the more subtle
residual velocity field allows us to explore further: gas inflows (e.g. Di
Teodoro Peek 2021; Genzel et al. 2023), bar and dynamical effect
of the bar/spiral structure (e.g. Grand et al. 2016; Monari et al. 2016;
Gómez et al. 2021), and even bending waves of the disc – seismic
ripple propagating through the disc due to perturbation by a recent
interaction with satellites (Bland-Hawthorn Tepper-Garcı́a 2021;
Tepper-Garcı́a, Bland-Hawthorn Freeman 2022; Urrejola-Mora
et al. 2022) or misaligned gas accretion (Khachaturyants et al. 2022).
In this paper, we report a new analysis of the bar structure in the
quasar host galaxy BRI 1335–0417 using ALMA Band 7 data of
the far-infrared (FIR) continuum (observed frame ∼ 869 μm or rest-
frame ∼ 160 μm) and ionized carbon [C II]. We also demonstrate that
the rotation-subtracted residual velocity field is consistent with the
dynamical imprint of a recent interaction by an external perturber,
which likely induced the bar and spiral density wave in the gas disc.
Throughout this paper, we assume a flat -dominated cold dark
matter cosmology with a present-day Hubble constant of H0 =
70 km s−1
Mpc−1
, and a density parameter of pressureless matter
M = 0.3.
2 OBSERVATION AND DATA REDUCTION
This study uses rest-frame 160 μm FIR continuum image and
[C II] line cube from the observation program #2017.1.00394.S
(PI = González López, Jorge), which was carried out on 2018 January
21. The data calibration and reduction details were described in
(Tsukui Iguchi 2021; Tsukui et al. 2023b). In order to accurately
quantify the elongated bar structure, both [C II] and FIR intensity
maps were convolved to have a circular-shaped beam (point spread
function; PSF) with the same resolution [full width half-maximum
(FWHM) = 0.195 arcsec = 1.3 kpc]. The [C II] line data are binned
in the spectral axis to have a spectral resolution of 20 km s−1
.
3 RESULTS AND DISCUSSION
In this section, we present the results of structural investigations in
the first two subsections and then investigations from the dynamical
point of view using first-order and higher-order [C II] kinematics in
the subsequent subsections.
3.1 Bar identification by the ellipse fitting
We employ the commonly used ellipse-fitting method to examine the
photometric structure of the disc (e.g. Jedrzejewski 1987; Wozniak
et al. 1995; Erwin 2005; Gadotti et al. 2007). We fit ellipses to
isophotes of the [C II] and FIR intensity images, with position angle
(PA) and ellipticity () allowed to vary for each ellipse and the central
position fixed to the best fit of the smallest ellipse. To estimate the
statistical uncertainty in our measurements, we performed the fitting
procedure 300 times, each time adding realistic correlated noise to
the original images. The noise properties are measured using the
noise auto-correlation function (Tsukui et al. 2023a).
The left column of Fig. 1 shows the ellipticity and PA of
the best-fitting ellipses as a function of radius. The right column
presents the best-fitting isophote ellipses overlaid on [C II] and FIR
images. The ellipticity profile of the best-fitting ellipses exhibits
a characteristic profile common to barred galaxies (Wozniak et al.
1995). At smaller radii, the ellipticity is small as the ellipses trace the
centrally concentrated light. Then the ellipticity reaches a maximum
as the ellipse aligns with the elongated bar shape. Subsequently, the
ellipticity decreases as the ellipse traces the disc more circular than
the bar. The PA changes slowly as the ellipse traces the bar and
rapidly changes at the end of the bar as the ellipse starts tracing the
disc because the disc PA is offset from the bar in most cases.1
In both [C II] and FIR continuum, the ellipticity reaches a max-
imum at the same radius within some uncertainty. Therefore, we
adopt the radius of the maximum ellipticity of [C II] as a fiducial
sky-projected bar length, R
sky
bar,max
= 3.1+0.2
−0.1 kpc. This bar length
is larger than the 2×FWHM of the beam, which is the required
minimum criterion for detecting the bar (Erwin 2018). Another way
to define the bar length from the ellipse fitting is the radius where
the PA changes by 5◦
relative to its value at the radius of maximum
ellipticity. This alternative definition provides slightly larger values,
R
sky
bar,PA=5deg = 3.5+0.3
−0.1 kpc yet similar to our adopted fiducial value,
confirming that the choice of the definition does not affect the
conclusion.
We find the intrinsic bar length Rint
bar,max
= 3.3+0.2
−0.2 kpc by the
analytical deprojection assuming a planer bar ellipse (Gadotti et al.
2007) and the disc inclination (37.3◦
) and PA (7.6◦
) estimated by
Tsukui Iguchi (2021). The bar length relative to the [C II] disc
scale length Rd = 1.83 ± 0.04 kpc (Tsukui Iguchi 2021) is larger
than stellar bars seen in nearby galaxies (Erwin 2019; their derived
1The elongated bar structure has a random orientation relative to the disc PA.
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Figure 1. Left column: Ellipticity (top) and PA (bottom) of isophote ellipses as a function of the ellipse radius (semimajor axis) of [C II] (blue) and FIR
(orange) images of BRI 1335–0417. The vertical lines indicate the radii of the maximum ellipticity for [C II] (blue) and FIR (orange). For each measurement,
1σ uncertainty is shown with a shaded region. The grey-shaded region indicates the PSF FWHM, where accurate ellipticity and PA estimates are not possible.
Right column: [C II] and FIR images of BRI 1335–0417 overlaid with the best-fitting isophote ellipses (black ellipses), the bar ellipse (a blue ellipse) and its
PA in the solid blue line. The disc kinematic PA (Tsukui Iguchi 2021) is also shown in the dashed blue line. The FWHM of PSF is shown in the bottom left
corner of both images.
scaling relation predicts a bar length of 1.7 ± 0.1 kpc given the same
disc scale length).
We note that the PA of the outermost isophote is misaligned with
the kinematic disc PA. The outer ellipses are influenced not only by
noise, as evidenced by the increased uncertainty shown in the bottom
left panel of Fig. 1, but also by the spiral structure and faint tidal tail-
like structure extending from north-east to south-west. Therefore,
in later analysis, we will use the kinematic disc PA rather than the
photometric isophote PA as the disc’s PA.
3.2 Interpretation of [C II] and FIR continuum bars
The [C II] line traces not only overall star formation but also multi-
phase gas distribution, from neutral gas (Herrera-Camus et al. 2018)
to molecular and ionized gas (Pineda et al. 2013). On the other hand,
the FIR continuum represents thermal emission from dust heated by
ultraviolet emission produced by young massive stars. Although the
FIR continuum is commonly used as the tracer for dust mass and SFR
(young massive stars heating the dust), the relationships of the single
band FIR continuum to these two quantities are complex depending
on the spatial temperature and opacity variation (da Cunha et al.
2021; Tsukui et al. 2023b). The FIR continuum is proportional to
the dust mass and SFR2
specifically in a limiting case of dust being
optically thin with a spatially constant temperature.
The ellipse fitting result confirms both [C II] and FIR continuum
images have elliptical elongated bar shapes, which are shown in
Fig. 2 along with the two-armed spiral confirmed in Tsukui Iguchi
2021 (projected on the sky). The configuration of the bar and spiral
2With several assumptions such that the dust is solely heated by the young
massive stars and archived single equilibrium temperature. Stellar initial mass
function and dust geometry are known.
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Figure 2. [C II] and FIR images of BRI 1335–0417 overlaid with our
identified bar ellipses (blue ellipse) and two-armed spiral structure identified
in Tsukui Iguchi (2021, black solid line). Contours start at 2σ in both maps
but are linearly spaced by 2σ for [C II] map and logarithmically spaced in
powers of 2 for FIR map (2σ, 4σ, 8σ,...).
is similar to the nearby grand-design spiral galaxies observed (e.g.
Stuber et al. 2023) and found in simulations (e.g. Baba 2015).
In the nearby Universe, not all barred galaxies show star formation
and gas reservoirs in the bar region. Star formation or gas lanes
along the bar region are preferentially found in gas-rich late-type
barred galaxies (Dı́az-Garcı́a et al. 2020; Fraser-McKelvie et al.
2020) and more massive gas-rich barred systems (Stuber et al.
2023). FIR continuum bars are often seen in high redshift (z ∼ 2–4)
submillimeter galaxies (Gullberg et al. 2019; Hodge et al. 2019),
implying that the star-forming gasious bar may be common in the
gas-rich early galaxies (Carilli Walter 2013).
Interestingly, there is a slight yet statistically significant offset in
PA of the bar ellipses between [C II] and FIR continuum (PA[C II] =
−15.9+4.0
−3.1, PAFIR = −6.9+4.2
−4.7). Also, the bar ellipse of [C II] is
more elongated than that of the FIR continuum ([C II] = 0.27+0.02
−0.02,
FIR = 0.39+0.03
−0.02). Although the rounder shape of the FIR bar may
be attributed to the significant AGN contribution to the FIR image
suggested by Tsukui et al. (2023b) these morphological differences,
if further confirmed by higher resolution data, may tell the dynamics
of the bar.
These differences may be consistent with the bar characteristics
commonly confirmed in local observations (Fraser-McKelvie et al.
2020) and simulation (Emsellem et al. 2015) – the compressed gas
flow (traced by [C II]) which usually forms a straight line into the
centre of the galaxy along the leading edge of the bar made up by
the stellar components (traced by FIR emission), making the [C II]
bar thinner than the FIR bar. The [C II] bar is also inclined towards
the leading edge of the FIR bar.
This interpretation requires two assumptions. (1) The spiral arm
in this galaxy is trailing as the majority of spiral galaxies are trailing
(e.g. Iye, Tadaki Fukumoto 2019). If so, the right (west) side in
Fig. 2 is the far side of the disc, and the disc rotates clockwise, given
that the north/south is the receding/approaching side of the disc (see
Fig. 3a). The bar ellipse of the [C II] line is displaced towards the
leading edge of the bar (on the downstream side of the gas motion). (2)
The FIR emission may trace more towards young stellar components
than interstellar medium (ISM) traced by [C II], as the FIR emission
can depend on the distribution of the dust (ISM) and young massive
stars which heat the dust. Especially in the early universe, ∼ 1 Gyr,
the main producers of dust grains are asymptotic giant branch (AGB)
stars or core-collapse supernovae (Gall, Hjorth Andersen 2011).
AGB stars start contributing at 10–100 Myr after the stellar evolution
of stars with the mass of 3–8 M while core-collapse supernovae
contribute after the lifetime of 10 Myr. Within the relatively longer
dynamical time-scale of the disc, 120 Myr, the stellar distribution
producing the dust would not have displaced relative to the dust
distribution.
As discussed in the next section, the stellar content is quite small
relative to gas, so the bar dynamics and formation may differ from
the nearby stellar-dominated bar paradigm.
3.3 Dynamical constraint from [C II] rotation curve
The detailed mass distribution within galaxies is an essential factor
for bar formation (e.g. Efstathiou, Lake Negroponte 1982; Fujii
et al. 2018; Bland-Hawthorn et al. 2023; Romeo, Agertz Renaud
2023). A disc-dominated system is prone to instability and bar
formation, while spherical structures such as dark matter and bulges
as well as the presence of gas can suppress the bar formation. In
this section, we derive a lower boundary on the disc fraction and
gas fraction using (1) the dynamical mass distribution estimated
by Tsukui Iguchi (2021) whose rotation curve is consistent with
the independent modelling by Roman-Oliveira, Fraternali Rizzo
(2023) and (2) the CO(2-1) line luminosity which traces molecular
gas mass (Jones et al. 2016). Then, we discuss the implication for
the bar formation in this galaxy.
Tsukui Iguchi (2021) decomposed the rotation curve into
contributions from the bulge and disc, assuming a de Vaucouleurs
mass distribution for the bulge and an exponential for the disc (with
the scale radius from the [C II] emission). The derived disc mass,
Mdisc = 4.9+1.7
−2.5 × 1010
M, is consistent with the lower limit of the
molecular gas mass, Mgas = 5.1 × 1010
M estimated by Jones et al.
(2016) assuming solar metalicity and a typical CO line ratio r21 =
LCO(2-1)/LCO(1-0) = 0.85 for submillimeter galaxies (Carilli Walter
2013), suggesting that the galaxy is baryon-dominated and gas-rich.
As Tsukui et al. (2023b) revealed the optical emission of BRI
1335–0417 is dominated by a quasar, using a typical r21 = 0.99
for quasars (Carilli Walter 2013) further reduces the estimated
molecular gas mass by 10 per cent to Mgas = 4.6 × 1010
M. Using
this lower limit on the molecular gas estimate, we derive a lower limit
for the disc mass fraction within the radius at which disc dynamics
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(a) (b) (c)
(d) (e)
Figure 3. (a) [C II] velocity field derived fitting a Gaussian at each spatial pixel of the data cube. (b) Best-fitting KINEMETRY model using odd Fourier series
(m = 1, 3, 5) to expand the azimuthal velocity profile. (c) Best-fitting KINEMETRY model using odd + even Fourier series (m = 1, 2, 3, 4, 5). (d) Residual map
subtracting the model with odd terms only (b) from the data velocity field (a). (e) Residual map subtracting the model with both odd and even terms (C) from
the data velocity field (a). In (a), (d), and (d), [C II] contours, bar ellipse, and two armed-spiral are overplotted in the same way as in Fig. 2.
dominates, 2.2Rd = 4.0 kpc,
fdisc =
vdisc(R)
vtotal(R)
2
R=2.2Rdisc
vgas(R)
vtotal(R)
2
R=2.2Rdisc
0.73 ± 0.07
(1)
where vtotal(2.2Rd) = 200 ± 10 km s−1
is the total circular velocity
at 2.2Rd (Tsukui Iguchi 2021), and vgas(2.2Rd) = 179 km s−1
is
the circular velocity of the exponential gas disc at 2.2Rd with the
lower limit mass.3
This lower limit on the disc mass fraction can
also be interpreted as a lower limit on the gas mass fraction and
baryon fraction in the disc, suggesting that the gravitational potential
of BRI 1335–0417 is dominated by gas rather than stars and dark
halo (see also Carilli et al. 2002; Riechers et al. 2008; suggesting gas
dominance in this galaxy).
Recent numerical studies have primarily focused on forming stellar
bars out of stellar discs alternating the orbits of disc stars (Bland-
Hawthorn et al. 2023) in which the gas delay the process. However,
a disc with such a high gas fraction as in BRI 1335–0417 may
behave differently. The dominant gas disc could potentially lead to
the formation of a gas bar (Barnes Tohline 2001), as opposed to
a dominant stellar disc forming a stellar bar, which then influences
the gas kinematics. Theoretically, an axisymmetric 100 per cent gas
disc is found to be able to form a self-gravitating stable gaseous bar
structure (Cazes Tohline 2000). This scenario seems plausible
explaining the prevalent high-redshift bar structures seen in far-
infrared emissions (Gullberg et al. 2019; Hodge et al. 2019) and
another high-z barred galaxy at z = 4.3 with an extreme gas fraction
3We assumed the dispersion supported disc with finite thickness and the scale
radius Rd of [C II] (Tsukui Iguchi 2021).
(Smail et al. 2023). However, whether the stars forming out of a
gaseous bar can lead to a stellar bar as we see in later epochs
(Guo et al. 2023; Le Conte et al. 2023) remains an open question,
as only idealised simulation experiments have been conducted
thus far.
3.4 Second order disc kinematics
We analyzed the [C II] gas velocity field of BRI 1335–0417 (Fig. 3a)
using KINEMETRY (Krajnović et al. 2006)4
to determine if there
is a dynamical imprint from a bar, recent interaction, and or in-
flow/outflow in the gas kinematics.KINEMETRY expands the velocity
field profile v(a, θ) along ellipses into Fourier series,
v(a, θ) = A0(a) +
N
m=1
Am(a) sin(mθ) + Bm(a) cos(mθ), (2)
where the ellipses are defined by the semimajor axis a, axis ratio
q, and PA from which azimuthal angle θ is measured. As the
velocity field of a rotating disc can be expressed by v(a, θ) = A0
+ B1(a)cos (θ) (Krajnović et al. 2006), the deviation from pure
rotational motion manifests as higher order coefficients (A1, A2,
B2,...). By this approach, we can investigate non-circular velocities
in a non-parametric manner, in contrast to the dynamical modelling
4See the derivation of [C II] velocity field (Tsukui et al. 2023b), Briefly, we
derived the velocity field by fitting a Gaussian function (including Hermite
parameters h3 and h4; Cappellari 2017) to the [C II] spectrum at each pixel,
where the three channels are available with the emission detected more than
3σ.
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method used in Tsukui Iguchi (2021), where they assumed a pure
circular rotation and bulge-disc mass profile.
We performed the KINEMETRY expansion of the azimuthal velocity
profile up to the fifth-order Fourier terms (m = 5) along concentric
ellipses. We used ellipses with a PA 7.6◦
and an axis ratio q = 0.79,
which are determined as the global kinematic PA using KINEMETRY
and the photometric axis ratio of the dust continuum distribution in
Tsukui Iguchi (2021), consistent with the independent measure-
ments by Roman-Oliveira, Fraternali Rizzo (2023). The centre of
each ellipse is fixed at the peak position of the continuum image,
which matches with the centre of rotation [see Fig. 3A Tsukui
Iguchi (2021)] and the optical quasar position (Tsukui et al. 2023b).
Fig. 3(b) shows the best-fitting expansion with odd-term harmon-
ics m = 1, 3, 5. The data-model residual (Fig. 3d) reveals the
significant even (m = 2) component, with two redshifted regions
and two blueshifted regions in symmetric positions. The redshifted
residuals spatially coincide with the two-armed spiral morphology
in the [C II] and FIR continuum maps. The features are already
visible in the velocity field before subtraction in Fig. 3(a); the
redshifted/blueshifted high velocity/low velocity are aligned with
spiral arms.
By definition, the m = 2 mode cannot be compensated by any
odd modes which are the orthogonal basis. This is illustrated by
Figs A1–A3. Fig. A1 shows the ellipses along which the azimuthal
velocity profiles are extracted by KINEMETRY. Figs A2 and A3 show
(top) the azimuthal velocity profiles v(θ) for ellipses at radii 0.54 and
0.68 arcsec with the best-fitting circular velocity A0 + B1cos θ and
the circular velocity residual v(θ) − A0 + B1cos θ with higher order
expansion with only odds terms and odds plus even terms (bottom),
clearly showing that m = 2 mode is required to reproduce the data
profile.
We also confirm that the m = 2 mode, with the amplitude of up
to ∼ 30–40 km s−1
, cannot be diminished by changing the PA and
axis ratio of the kinematic ellipses by ±20◦
and ±0.1, respectively
(Fig. A4). The addition of the even components fully characterizes
the velocity field of the BRI 1335–0417 [see the best-fitting harmonic
expansion in Fig. 3(c)] leaving only a small data-model residual
over the disc shown in Fig. 3(e). Recently, Bagge et al. (2023) also
explored the importance of the even components in spatially resolved
gas kinematics for galaxies at intermediate redshift z ∼ 0.3.
3.5 Interpretation of the m = 2 mode in velocity field
We conclude that the observed m = 2 kinematic mode in the velocity
residual is less likely due to inflow or outflow, as symmetric flow
would show line of sight velocity residuals with the opposite sign in
symmetric positions (Di Teodoro Peek 2021; Genzel et al. 2023),
leaving the peculiar possibility where the residual on one side is due
to outflow while the opposite side is due to inflow. Similarly, it is
unlikely due to in-plane motion induced by the dynamical influence
of spiral and bar structures (e.g. Grand et al. 2016; Monari et al.
2016; Gómez et al. 2021). The analytical model suggests a m-fold
symmetric mass density structure would only induce m − 1 or m + 1
velocity field distortions (Canzian 1993; Schoenmakers, Franx de
Zeeuw 1997), inconsistent with the observed m = 2 mode velocity
residual for a m = 2 spiral and bar density structures in the galaxy.
Also, the m = 2 mode velocity residual cannot be attributed to a PA
change of the disc due to disc tilting.
Using an analytic model for a galaxy with similar rotational
velocity and inclination to BRI 1335–0417, Gómez et al. (2021)
show that the radial velocity induced by the spiral density structure
is small (10 km s−1
) compared to the disc vertical velocity caused
by an interaction. Assuming the line of sight velocity residual of
the m = 2 mode, ∼ 35 km s−1
(Fig. 3d), is purely due to in-plane
radial motion, the induced radial velocity would be 57 km s−1
after
inclination correction. With and without inclination correction the
magnitude of the velocity residual seems too large to attribute for the
radial motion caused by the spiral structure (e.g. Grand et al. 2016;
Monari et al. 2016).
A more plausible explanation for the observed m = 2 mode
signature is vertical motion relative to the disc (disc bending mode)
induced by external forces, such as recent interactions with satellite
galaxies (e.g. Gómez et al. 2017; Bland-Hawthorn Tepper-Garcı́a
2021) or misaligned gas accretions (Khachaturyants et al. 2022).
Strikingly, the kinematic m = 2 mode in BRI 1335–0417 spatially
coincides with the spiral structure in the intensity map, as shown in
Fig. 3(d). This overlap is consistent with the vertical wave of stellar
and gas discs induced by satellite interactions in some simulations
(Tepper-Garcı́a, Bland-Hawthorn Freeman 2022). The simulations
reveal the m = 1 mode in the disc vertical velocity develops
∼100 Myr after the Milky-Way-like galaxy is perturbed by the high-
speed encounter of the Sagittarius dwarf system, followed by the
development of the m = 2 mode vertical velocity as soon as 200–
400 Myr (Bland-Hawthorn Tepper-Garcı́a 2021; Tepper-Garcı́a,
Bland-Hawthorn Freeman 2022). The vertical velocity pattern
initially aligns with the spiral pattern in density and then decouples.
The observed co-spatial spiral arm patterns in velocity residual
and intensity (Fig. 3d) are consistent with the simulation of bending
waves induced by interactions, or at least imply a common cause
for the two. Given that BRI 1335–0417 has a gas-rich, dynamically
hot disc with velocity dispersion of ∼70 km s−1
(Tsukui Iguchi
2021), conditions typically unfavourable for spontaneous spiral
arm formation (Elmegreen Elmegreen 2014), it is reasonable to
interpret that the external perturbation responsible for the m = 2
bending mode induced the observed spiral arms even in a dynamically
hot disc (Law et al. 2012) and potentially formed bar (Łokas et al.
2014, 2016). The disc is turbulent but still baryon-dominated and
gravitationally unstable (Tsukui Iguchi 2021), making it prone to
forming such substructures through perturbations (Law et al. 2012).
The gas velocity dispersion, σ, of BRI 1335–0417 is estimated to
be 71+14
−11 km s−1
(Tsukui Iguchi 2021). This value is relatively high
compared to average values at lower redshifts (45 km s−1
at z = 2.3,
30 km s−1
at z = 0.9; Übler et al. 2019) but is in agreement with the
scatter seen around cosmic noon (Kassin et al. 2012; Wisnioski et al.
2015; Übler et al. 2019; Wisnioski et al. 2019). Using the EAGLE
simulations, Jiménez et al. (2023) highlights the importance of the
gas accretion rate and its relative orientation to the disc in driving the
redshift evolution of disc velocity dispersion. The gas accretion (and
accompanying satellites) with a large angle relative to the disc plane
effectively increases the velocity dispersion of the disc. In general
bending mode (buckling instability) is suppressed for a disc with
isotropic velocity dispersion (Toomre 1964; Araki 1985; Merritt
Sellwood 1994, see for review Sellwood 2013) which may hold for
high-redshift galaxies (Genzel et al. 2017; Genzel et al. 2023). The
bending wave induced by the vertical perturbation of the high-angle
accreters may be immediately damped and contribute to the kinetic
energy of the disc velocity dispersion.
4 CONCLUSION
We identify an elongated bar-like structure in the z = 4.4 spiral
galaxy BRI 1335–0417 using both [C II] and rest-frame 160 μm
FIR images by fitting ellipses to the isophotes. The variation of
ellipticity and PA shows the characteristic profile of barred galaxies.
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7. Bar structure and disc bending wave at z = 4.4 8947
MNRAS 527, 8941–8949 (2024)
The identified bar, 3.3+0.2
−0.2 kpc long in radius, appears to bridge the
two arm spirals identified in the previous study (Tsukui Iguchi
2021). When compared to the disc scale length, the bar length is
larger than stellar bars in nearby galaxies (Erwin 2019).
The [C II] bar is more elongated than the FIR bar and displaced
towards the leading edge of the FIR bar (at the downstream side of
the gas motion), assuming the spiral arms of BRI 1335–0417 are
trailing spiral arms. If we attribute the structural difference of FIR
and [C II] to the fact that FIR emission can depend on the distribution
of both dust (ISM roughly traced by [C II]) and young massive stars
heating the dust, the observations seem to align with the established
picture from both observations and simulations – the compressed
gas flow (traced by [C II]) forms a straight line into the centre of the
galaxy along the leading edge of the young stellar bar (more traced
by FIR emission).
The galaxy is shown to have a significant gas fraction (73
per cent), hosting the star-forming gas bar, which prevents us from
assuming the presence of a stellar bar dominating the gravitational
potential and influences the gas bar kinematics. Along with this
object, the abundant bar-like structures in FIR continuum observed
in bright sub-millimetre galaxies (Gullberg et al. 2019; Hodge et al.
2019) and another example high-redshift barred galaxy at z = 4.3
with an extremely high gas fraction (Smail et al. 2023) may prompt a
different perspective on the bar formation and dynamics rather than
simulations focused on how disc stars form stellar bars. The dominant
gas disc, by itself gravitationally unstable, potentially leads to the
formation of a gas bar (Barnes Tohline 2001), as an axisymmetric
100 per cent gas disc is theoretically proven to form a self-gravitating
stable gaseous bar structure (Cazes Tohline 2000).
By applying a harmonic expansion of azimuthal profiles of the
[C II] velocity field with KINEMETRY we reveal a dominant m = 2
mode with the amplitude of up to ∼30–40 km s−1
in the velocity
residual. The m = 2 mode cannot be explained by large-scale
inflow/outflow or the non-circular motions caused by bar/spirals,
which generally produce odd-numbered modes (e.g. Canzian 1993;
Schoenmakers, Franx de Zeeuw 1997). Therefore we interpret
the m = 2 mode as vertical motion relative to the disc (disc bending
wave). The redshifted velocity regions contributing to the m = 2 mode
coincide spatially with the spiral arms, consistent with the scenario
where the galactic disc is perturbed by an interaction creating the
initially co-spatial spiral density wave and vertical bending mode
in the disc (e.g. Bland-Hawthorn Tepper-Garcı́a 2021; Tepper-
Garcı́a, Bland-Hawthorn Freeman 2022).
As it is assumed that a gas disc is stable for the bending mode
(buckling instability), the m = 2 mode velocity perturbation and
spiral arms are likely to be induced by a recent interaction and/or gas
accretion. It is natural to suppose that such an interaction would also
activate the high star formation activity.
For the first time, this study detects an unambiguous m = 2 mode
in a disc at high redshift (z 4), lending support to the use of
disc seismic ripple as evidence of a recent strong perturbation. With
further numerical simulations tuned for galaxies with realistic gas,
halo, and stellar masses and gas accretion histories, the m = 2 mode
may provide a useful constraint on the exact timing and primary
origin of external perturbations.
ACKNOWLEDGEMENTS
TT is grateful to the conference organizers of Galactic Bars: driving
and decoding galaxy evolution held in Granada, Spain in 2023 July,
which greatly helped in writing this paper and Trevor Mendel for
encouraging me to attend. TT also thanks Camila de Sá-Freitas, Karin
Menedez Delmestre, Ewa Luiza Lokas, and Andreas Burkert for
insightful discussions. This research was supported by the Australian
Research Council Centre of Excellence for All Sky Astrophysics in
3 Dimensions (ASTRO 3D), through project number CE170100013.
Data analysis was partly carried out on the Multi-wavelength Data
Analysis System operated by the Astronomy Data Center (ADC),
National Astronomical Observatory of Japan. This paper makes use
of the following ALMA data: ADS/JAO.ALMA#2017.1.00394.S.
ALMA is a partnership of ESO (representing its member states),
NSF (USA), and NINS (Japan), together with NRC (Canada), NSC
and ASIAA (Taiwan) and KASI (Republic of Korea), in cooperation
with the Republic of Chile. The Joint ALMA Observatory is operated
by ESO, AUI/NRAO, and NAOJ. Finally, TT thanks Takaho Masai
for his kind support at NAOJ.
DATA AVAILABILITY
The ALMA data we use in this work are publicly available in https:
//almascience.nrao.edu/aq/.
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APPENDIX A: SUPPLEMENTAL INFORMATION
OF KINEMETRY ANALYSIS
In this section, we provide the detailed results of the KINEMETRY
analysis to verify the presence of m = 2 mode. Fig. A1 shows
the ellipses to extract the azimuthal profile of the velocity field.
Figs A2 and A3 illustrate the harmonic expansion of the azimuthal
velocity profiles at two specific radii: 0.54 and 0.68 arcsec. For the
sake of visualization, the pure rotational motion (top: blue line) is
subtracted from the original velocity profile (top: black points) and
we have shown a higher-order expansion for the residual (bottom:
black points). The expansion involves odds terms with or without
even terms up to m = 5 modes (shown as red solid and dashed lines
respectively). Even terms, especially m = 2 mode are required to
reproduce the velocity fields. The dominance of the m = 2 relative
to the other modes obtained by expansion with full terms (odds plus
even) is shown in Fig. A4; the m = 2 is dominant after 0.4 arcsec and,
opposed to other odds modes, is not diminished by the vast change
of PA and ellipticity of sampling ellipses.
Figure A1. Blue points: Ellipses and azimuthal data sampling of each ellipse
used for KINEMETRY analysis overlain on the BRI 1335–0417 velocity field.
Black solid lines show ellipses with a radius of 0.54 arcsec and 0.68 arcsec
whose velocity profiles are shown in Figs A2 and A3.
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