Supernova (SN) plays an important role in galaxy formation and evolution. In high-resolution galaxy simulations using massively
parallel computing, short integration time-steps for SNe are serious bottlenecks. This is an urgent issue that needs to be resolved
for future higher-resolution galaxy simulations. One possible solution would be to use the Hamiltonian splitting method, in
which regions requiring short time-steps are integrated separately from the entire system. To apply this method to the particles
affected by SNe in a smoothed particle hydrodynamics simulation, we need to detect the shape of the shell on and within which
such SN-affected particles reside during the subsequent global step in advance. In this paper, we develop a deep learning model,
3D-Memory In Memory (3D-MIM), to predict a shell expansion after a SN explosion. Trained on turbulent cloud simulations
with particle mass mgas = 1 M, the model accurately reproduces the anisotropic shell shape, where densities decrease by over
10 per cent by the explosion. We also demonstrate that the model properly predicts the shell radius in the uniform medium
beyond the training data set of inhomogeneous turbulent clouds. We conclude that our model enables the forecast of the shell
and its interior where SN-affected particles will be present.
Measuring the Hubble constant with kilonovae using the expanding photosphere ...Sérgio Sacani
While gravitational wave (GW) standard sirens from neutron star (NS) mergers have been proposed to offer good measurements of
the Hubble constant, we show in this paper how a variation of the expanding photosphere method (EPM) or spectral-fitting expanding
atmosphere method, applied to the kilonovae (KNe) associated with the mergers, can provide an independent distance measurement
to individual mergers that is potentially accurate to within a few percent. There are four reasons why the KN-EPM overcomes the
major uncertainties commonly associated with this method in supernovae: (1) the early continuum is very well-reproduced by a
blackbody spectrum, (2) the dilution effect from electron scattering opacity is likely negligible, (3) the explosion times are exactly
known due to the GW detection, and (4) the ejecta geometry is, at least in some cases, highly spherical and can be constrained from
line-shape analysis. We provide an analysis of the early VLT/X-shooter spectra AT2017gfo showing how the luminosity distance can
be determined, and find a luminosity distance of DL = 44.5 ± 0.8 Mpc in agreement with, but more precise than, previous methods.
We investigate the dominant systematic uncertainties, but our simple framework, which assumes a blackbody photosphere, does not
account for the full time-dependent three-dimensional radiative transfer effects, so this distance should be treated as preliminary. The
luminosity distance corresponds to an estimated Hubble constant of H0 = 67.0 ± 3.6 km s−1 Mpc−1
, where the dominant uncertainty
is due to the modelling of the host peculiar velocity. We also estimate the expected constraints on H0 from future KN-EPM-analysis
with the upcoming O4 and O5 runs of the LIGO collaboration GW-detectors, where five to ten similar KNe would yield 1% precision
cosmological constraints.
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.
A Comprehensive Theory for Neutron Star and Black Hole Kicks and Induced SpinsSérgio Sacani
Using twenty long-term 3D core-collapse supernova simulations, we find that lower compactness progenitors that explode quasi-spherically due to the short delay to explosion experience smaller neutron
star recoil kicks in the ∼100−200 km s−1
range, while higher compactness progenitors that explode
later and more aspherically leave neutron stars with kicks in the ∼300−1000 km s−1
range. In addition, we find that these two classes are correlated with the gravitational mass of the neutron star.
This correlation suggests that the survival of binary neutron star systems may in part be due to their
lower kick speeds. We also find a correlation of the kick with both the mass dipole of the ejecta
and the explosion energy. Furthermore, one channel of black hole birth leaves masses of ∼10 M⊙, is
not accompanied by a neutrino-driven explosion, and experiences small kicks. A second is through
a vigorous explosion that leaves behind a black hole with a mass of ∼3.0 M⊙ kicked to high speeds.
We find that the induced spins of nascent neutron stars range from seconds to ∼10 milliseconds and
that a spin/kick correlation for pulsars emerges naturally. We suggest that if an initial spin biases
the explosion direction, a spin/kick correlation is a common byproduct of the neutrino mechanism of
core-collapse supernovae. Finally, the induced spin in explosive black hole formation is likely large and
in the collapsar range. This new 3D model suite provides a greatly expanded perspective and appears
to explain some observed pulsar properties by default.
The hazardous km-sized NEOs of the next thousands of yearsSérgio Sacani
This document discusses methods for assessing the long-term impact risk of km-sized near-Earth objects (NEOs) over thousands of years. It analyzes the evolution of the Minimum Orbit Intersection Distance (MOID) between NEOs and Earth to identify objects that remain in close proximity for extended periods. It then estimates the probability of a deep Earth encounter during these low-MOID periods based on the growth of orbital uncertainties over time. This allows the authors to rank km-sized NEOs by their long-term impact hazard and identify targets that warrant further observation and analysis.
This document describes an algorithm developed to simulate the fiber assignment process for the Maunakea Spectroscopic Explorer (MSE) telescope. The algorithm was designed to maximize spatial completeness by assigning fibers to target galaxies based on their positions and the constraints of the Echidna fiber positioner. The algorithm draws upon methods used by the Galaxy And Mass Assembly (GAMA) survey and involves looping through galaxy targets to determine the closest available fiber for each one. Testing with over 450,000 galaxies from a cosmological simulation showed promising early results in achieving high completeness across the survey fields.
3D stellar evolution: hydrodynamic simulations of a complete burning phase in...Sérgio Sacani
Our knowledge of stellar evolution is driven by one-dimensional (1D) simulations. 1D models, however, are severely limited by uncertainties on the exact behaviour of many multidimensional phenomena occurring inside stars, affecting their structure and e volution. Recent adv ances in computing resources have allowed small sections of a star to be reproduced with multi-D hydrodynamic models, with an unprecedented degree of detail and realism. In this work, we present a set of 3D simulations of a conv ectiv e neon-burning shell in a 20 M star run for the first time continuously from its early development through to complete fuel exhaustion, using unaltered input conditions from a 321D-guided 1D stellar model. These simulations help answer some open questions in stellar physics. In particular, they show that conv ectiv e re gions do not grow indefinitely due to entrainment of fresh material, but fuel consumption pre v ails o v er entrainment, so when fuel is e xhausted conv ection also starts decaying. Our results show convergence between the multi-D simulations and the new 321D-guided 1D model, concerning the amount of conv ectiv e boundary mixing to include in stellar models. The size of the conv ectiv e zones in a star strongly affects its structure and e volution; thus, re vising their modelling in 1D will have important implications for the life and fate of stars. This will thus affect theoretical predictions related to nucleosynthesis, supernova explosions, and compact remnants.
Prospects for Detecting Gaps in Globular Cluster Stellar Streams in External ...Sérgio Sacani
Stellar streams form through the tidal disruption of satellite galaxies or globular clusters orbiting a
host galaxy. Globular cluster streams are exciting since they are thin (dynamically cold) and, therefore
sensitive to perturbations from low-mass subhalos. Since the subhalo mass function differs depending
on the dark matter composition, these gaps can provide unique constraints on dark matter models.
However, current samples are limited to the Milky Way. With its large field of view, deep imaging
sensitivity, and high angular resolution, the upcoming Nancy Grace Roman Space Telescope (Roman)
presents a unique opportunity to increase the number of observed streams and gaps significantly. This
paper presents a first exploration of the prospects for detecting gaps in streams in M31 and other
nearby galaxies with resolved stars. We simulate the formation of gaps in a Palomar-5-like stream
and generate mock observations of these gaps with background stars in M31 and the foreground Milky
Way stellar fields. We assess Roman’s ability to detect gaps out to 10 Mpc through visual inspection
and with the gap-finding tool FindTheGap. We conclude that gaps of ≈ 1.5 kpc in streams that are
created from subhalos of masses ≥ 5×106 M⊙ are detectable within a 2–3 Mpc volume in exposures of
1000s–1 hour. This volume contains ≈ 150 galaxies, including ≈ 8 galaxies with luminosities > 109 L⊙.
Large samples of stream gaps in external galaxies will open up a new era of statistical analyses of gap
characteristics in stellar streams and help constrain dark matter models.
Locating Hidden Exoplanets in ALMA Data Using Machine LearningSérgio Sacani
Exoplanets in protoplanetary disks cause localized deviations from Keplerian velocity in channel maps of
molecular line emission. Current methods of characterizing these deviations are time consuming,and there is no
unified standard approach. We demonstrate that machine learning can quickly and accurately detect the presence of
planets. We train our model on synthetic images generated from simulations and apply it to real observations to
identify forming planets in real systems. Machine-learning methods, based on computer vision, are not only
capable of correctly identifying the presence of one or more planets, but they can also correctly constrain the
location of those planets.
Measuring the Hubble constant with kilonovae using the expanding photosphere ...Sérgio Sacani
While gravitational wave (GW) standard sirens from neutron star (NS) mergers have been proposed to offer good measurements of
the Hubble constant, we show in this paper how a variation of the expanding photosphere method (EPM) or spectral-fitting expanding
atmosphere method, applied to the kilonovae (KNe) associated with the mergers, can provide an independent distance measurement
to individual mergers that is potentially accurate to within a few percent. There are four reasons why the KN-EPM overcomes the
major uncertainties commonly associated with this method in supernovae: (1) the early continuum is very well-reproduced by a
blackbody spectrum, (2) the dilution effect from electron scattering opacity is likely negligible, (3) the explosion times are exactly
known due to the GW detection, and (4) the ejecta geometry is, at least in some cases, highly spherical and can be constrained from
line-shape analysis. We provide an analysis of the early VLT/X-shooter spectra AT2017gfo showing how the luminosity distance can
be determined, and find a luminosity distance of DL = 44.5 ± 0.8 Mpc in agreement with, but more precise than, previous methods.
We investigate the dominant systematic uncertainties, but our simple framework, which assumes a blackbody photosphere, does not
account for the full time-dependent three-dimensional radiative transfer effects, so this distance should be treated as preliminary. The
luminosity distance corresponds to an estimated Hubble constant of H0 = 67.0 ± 3.6 km s−1 Mpc−1
, where the dominant uncertainty
is due to the modelling of the host peculiar velocity. We also estimate the expected constraints on H0 from future KN-EPM-analysis
with the upcoming O4 and O5 runs of the LIGO collaboration GW-detectors, where five to ten similar KNe would yield 1% precision
cosmological constraints.
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.
A Comprehensive Theory for Neutron Star and Black Hole Kicks and Induced SpinsSérgio Sacani
Using twenty long-term 3D core-collapse supernova simulations, we find that lower compactness progenitors that explode quasi-spherically due to the short delay to explosion experience smaller neutron
star recoil kicks in the ∼100−200 km s−1
range, while higher compactness progenitors that explode
later and more aspherically leave neutron stars with kicks in the ∼300−1000 km s−1
range. In addition, we find that these two classes are correlated with the gravitational mass of the neutron star.
This correlation suggests that the survival of binary neutron star systems may in part be due to their
lower kick speeds. We also find a correlation of the kick with both the mass dipole of the ejecta
and the explosion energy. Furthermore, one channel of black hole birth leaves masses of ∼10 M⊙, is
not accompanied by a neutrino-driven explosion, and experiences small kicks. A second is through
a vigorous explosion that leaves behind a black hole with a mass of ∼3.0 M⊙ kicked to high speeds.
We find that the induced spins of nascent neutron stars range from seconds to ∼10 milliseconds and
that a spin/kick correlation for pulsars emerges naturally. We suggest that if an initial spin biases
the explosion direction, a spin/kick correlation is a common byproduct of the neutrino mechanism of
core-collapse supernovae. Finally, the induced spin in explosive black hole formation is likely large and
in the collapsar range. This new 3D model suite provides a greatly expanded perspective and appears
to explain some observed pulsar properties by default.
The hazardous km-sized NEOs of the next thousands of yearsSérgio Sacani
This document discusses methods for assessing the long-term impact risk of km-sized near-Earth objects (NEOs) over thousands of years. It analyzes the evolution of the Minimum Orbit Intersection Distance (MOID) between NEOs and Earth to identify objects that remain in close proximity for extended periods. It then estimates the probability of a deep Earth encounter during these low-MOID periods based on the growth of orbital uncertainties over time. This allows the authors to rank km-sized NEOs by their long-term impact hazard and identify targets that warrant further observation and analysis.
This document describes an algorithm developed to simulate the fiber assignment process for the Maunakea Spectroscopic Explorer (MSE) telescope. The algorithm was designed to maximize spatial completeness by assigning fibers to target galaxies based on their positions and the constraints of the Echidna fiber positioner. The algorithm draws upon methods used by the Galaxy And Mass Assembly (GAMA) survey and involves looping through galaxy targets to determine the closest available fiber for each one. Testing with over 450,000 galaxies from a cosmological simulation showed promising early results in achieving high completeness across the survey fields.
3D stellar evolution: hydrodynamic simulations of a complete burning phase in...Sérgio Sacani
Our knowledge of stellar evolution is driven by one-dimensional (1D) simulations. 1D models, however, are severely limited by uncertainties on the exact behaviour of many multidimensional phenomena occurring inside stars, affecting their structure and e volution. Recent adv ances in computing resources have allowed small sections of a star to be reproduced with multi-D hydrodynamic models, with an unprecedented degree of detail and realism. In this work, we present a set of 3D simulations of a conv ectiv e neon-burning shell in a 20 M star run for the first time continuously from its early development through to complete fuel exhaustion, using unaltered input conditions from a 321D-guided 1D stellar model. These simulations help answer some open questions in stellar physics. In particular, they show that conv ectiv e re gions do not grow indefinitely due to entrainment of fresh material, but fuel consumption pre v ails o v er entrainment, so when fuel is e xhausted conv ection also starts decaying. Our results show convergence between the multi-D simulations and the new 321D-guided 1D model, concerning the amount of conv ectiv e boundary mixing to include in stellar models. The size of the conv ectiv e zones in a star strongly affects its structure and e volution; thus, re vising their modelling in 1D will have important implications for the life and fate of stars. This will thus affect theoretical predictions related to nucleosynthesis, supernova explosions, and compact remnants.
Prospects for Detecting Gaps in Globular Cluster Stellar Streams in External ...Sérgio Sacani
Stellar streams form through the tidal disruption of satellite galaxies or globular clusters orbiting a
host galaxy. Globular cluster streams are exciting since they are thin (dynamically cold) and, therefore
sensitive to perturbations from low-mass subhalos. Since the subhalo mass function differs depending
on the dark matter composition, these gaps can provide unique constraints on dark matter models.
However, current samples are limited to the Milky Way. With its large field of view, deep imaging
sensitivity, and high angular resolution, the upcoming Nancy Grace Roman Space Telescope (Roman)
presents a unique opportunity to increase the number of observed streams and gaps significantly. This
paper presents a first exploration of the prospects for detecting gaps in streams in M31 and other
nearby galaxies with resolved stars. We simulate the formation of gaps in a Palomar-5-like stream
and generate mock observations of these gaps with background stars in M31 and the foreground Milky
Way stellar fields. We assess Roman’s ability to detect gaps out to 10 Mpc through visual inspection
and with the gap-finding tool FindTheGap. We conclude that gaps of ≈ 1.5 kpc in streams that are
created from subhalos of masses ≥ 5×106 M⊙ are detectable within a 2–3 Mpc volume in exposures of
1000s–1 hour. This volume contains ≈ 150 galaxies, including ≈ 8 galaxies with luminosities > 109 L⊙.
Large samples of stream gaps in external galaxies will open up a new era of statistical analyses of gap
characteristics in stellar streams and help constrain dark matter models.
Locating Hidden Exoplanets in ALMA Data Using Machine LearningSérgio Sacani
Exoplanets in protoplanetary disks cause localized deviations from Keplerian velocity in channel maps of
molecular line emission. Current methods of characterizing these deviations are time consuming,and there is no
unified standard approach. We demonstrate that machine learning can quickly and accurately detect the presence of
planets. We train our model on synthetic images generated from simulations and apply it to real observations to
identify forming planets in real systems. Machine-learning methods, based on computer vision, are not only
capable of correctly identifying the presence of one or more planets, but they can also correctly constrain the
location of those planets.
Locating Hidden Exoplanets in ALMA Data Using Machine LearningSérgio Sacani
Exoplanets in protoplanetary disks cause localized deviations from Keplerian velocity in channel
maps of molecular line emission. Current methods of characterizing these deviations are time consuming, and there is no unified standard approach. We demonstrate that machine learning can quickly
and accurately detect the presence of planets. We train our model on synthetic images generated from
simulations and apply it to real observations to identify forming planets in real systems. Machine
learning methods, based on computer vision, are not only capable of correctly identifying the presence
of one or more planets, but they can also correctly constrain the location of those planets.
The first X-ray look at SMSS J114447.77-430859.3: the most luminous quasar in...Sérgio Sacani
SMSS J114447.77-430859.3 (z = 0.83) has been identified in the SkyMapper Southern Survey as the most luminous quasar in
the last ∼ 9 Gyr . In this paper, we report on the eROSITA/Spectrum–Roentgen–Gamma (SRG) observations of the source from
the eROSITA All Sky Survey, along with presenting results from recent monitoring performed using Swift, XMM-Newton, and
NuSTAR. The source shows a clear variability by factors of ∼10 and ∼2.7 overtime-scales of a year and of a few days,respectively.
When fit with an absorbed power law plus high-energy cutoff, the X-ray spectra reveal a = 2.2 ± 0.2 and Ecut = 23+26
−5 keV
. Assuming Comptonization, we estimate a coronal optical depth and electron temperature of τ = 2.5 − 5.3 (5.2 − 8) and
kT = 8 − 18 (7.5 − 14) keV , respectively, for a slab (spherical) geometry. The broadband SED is successfully modelled by
assuming either a standard accretion disc illuminated by a central X-ray source, or a thin disc with a slim disc emissivity profile.
The former model results in a black hole mass estimate of the order of 1010 M , slightly higher than prior optical estimates;
meanwhile, the latter model suggests a lower mass. Both models suggest sub-Eddington accretion when assuming a spinning
black hole, and a compact (∼ 10 rg ) X-ray corona. The measured intrinsic column density and the Eddington ratio strongly
suggest the presence of an outflow driven by radiation pressure. This is also supported by variation of absorption by an order of
magnitude over the period of ∼ 900 d .
Identification of Superclusters and Their Properties in the Sloan Digital Sky...Sérgio Sacani
Superclusters are the largest massive structures in the cosmic web, on tens to hundreds of megaparsec scales. They
are the largest assembly of galaxy clusters in the Universe. Apart from a few detailed studies of such structures,
their evolutionary mechanism is still an open question. In order to address and answer the relevant questions, a
statistically significant, large catalog of superclusters covering a wide range of redshifts and sky areas is essential.
Here, we present a large catalog of 662 superclusters identified using a modified friends-of-friends algorithm
applied on the WHL (Wen–Han–Liu) cluster catalog within a redshift range of 0.05 z 0.42. We name the most
massive supercluster at z ∼ 0.25 as the Einasto Supercluster. We find that the median mass of superclusters is
∼5.8 × 10 15 Me and the median size ∼65 Mpc. We find that the supercluster environment slightly affects the
growth of clusters. We compare the properties of the observed superclusters with the mock superclusters extracted
from the Horizon Run 4 cosmological simulation. The properties of the superclusters in the mocks and
observations are in broad agreement. We find that the density contrast of a supercluster is correlated with its
maximum extent with a power-law index, α ∼ −2. The phase-space distribution of mock superclusters shows that,
on average, ∼90% of part of a supercluster has a gravitational influence on its constituents. We also show the mock
halos’ average number density and peculiar velocity profiles in and around the superclusters.
This document summarizes the results of an MHD simulation coupled with a radiation transport model to simulate X-ray spectra from an accreting black hole. Key points:
- For the first time, the simulation is able to reproduce the main components seen in observed X-ray spectra, including a thermal peak, power-law tail, reflection hump, and iron line, by varying only the mass accretion rate.
- The temperature in the corona varies from 10 keV near the disk to over 100 keV in low-density regions, producing the hard X-ray emission through inverse-Compton scattering.
- Even as the disk's reflection edge varies from the horizon out to 6 gravitational radii with decreasing accretion
Continuum emission from within the plunging region of black hole discsSérgio Sacani
The thermal continuum emission observed from accreting black holes across X-ray bands has the potential to be leveraged as a
powerful probe of the mass and spin of the central black hole. The vast majority of existing ‘continuum fitting’ models neglect
emission sourced at and within the innermost stable circular orbit (ISCO) of the black hole. Numerical simulations, however,
find non-zero emission sourced from these regions. In this work, we extend existing techniques by including the emission
sourced from within the plunging region, utilizing new analytical models that reproduce the properties of numerical accretion
simulations. We show that in general the neglected intra-ISCO emission produces a hot-and-small quasi-blackbody component,
but can also produce a weak power-law tail for more extreme parameter regions. A similar hot-and-small blackbody component
has been added in by hand in an ad hoc manner to previous analyses of X-ray binary spectra. We show that the X-ray spectrum
of MAXI J1820+070 in a soft-state outburst is extremely well described by a full Kerr black hole disc, while conventional
models that neglect intra-ISCO emission are unable to reproduce the data. We believe this represents the first robust detection of
intra-ISCO emission in the literature, and allows additional constraints to be placed on the MAXI J1820 + 070 black hole spin
which must be low a• < 0.5 to allow a detectable intra-ISCO region. Emission from within the ISCO is the dominant emission
component in the MAXI J1820 + 070 spectrum between 6 and 10 keV, highlighting the necessity of including this region. Our
continuum fitting model is made publicly available.
Large scale mass_distribution_in_the_illustris_simulationSérgio Sacani
Observations at low redshifts thus far fail to account for all of the baryons expected in the
Universe according to cosmological constraints. A large fraction of the baryons presumably
resides in a thin and warm–hot medium between the galaxies, where they are difficult to observe
due to their low densities and high temperatures. Cosmological simulations of structure
formation can be used to verify this picture and provide quantitative predictions for the distribution
of mass in different large-scale structure components. Here we study the distribution
of baryons and dark matter at different epochs using data from the Illustris simulation. We
identify regions of different dark matter density with the primary constituents of large-scale
structure, allowing us to measure mass and volume of haloes, filaments and voids. At redshift
zero, we find that 49 per cent of the dark matter and 23 per cent of the baryons are within
haloes more massive than the resolution limit of 2 × 108 M⊙. The filaments of the cosmic
web host a further 45 per cent of the dark matter and 46 per cent of the baryons. The remaining
31 per cent of the baryons reside in voids. The majority of these baryons have been transported
there through active galactic nuclei feedback. We note that the feedback model of Illustris
is too strong for heavy haloes, therefore it is likely that we are overestimating this amount.
Categorizing the baryons according to their density and temperature, we find that 17.8 per cent
of them are in a condensed state, 21.6 per cent are present as cold, diffuse gas, and 53.9 per cent
are found in the state of a warm–hot intergalactic medium.
MUSE sneaks a peek at extreme ram-pressure stripping events. I. A kinematic s...Sérgio Sacani
- MUSE observations of the galaxy ESO137-001 reveal an extended gaseous tail over 30 kpc long traced by H-alpha emission, providing evidence of an extreme ram pressure stripping event as the galaxy falls into the massive Norma galaxy cluster.
- Analysis of the H-alpha kinematics and stellar velocity field show that ram pressure has removed the interstellar medium from the outer disk while the primary tail is still fed by gas from the galaxy center, with gravitational interactions not appearing to be the main mechanism of gas removal.
- The stripped gas retains evidence of the disk's rotational velocity out to around 20 kpc downstream, indicating the galaxy is moving radially along the plane of the sky, while
This document describes observations of the galaxy ESO137-001 using the MUSE instrument on the VLT. The key points are:
1) MUSE observations reveal an extended gas tail stretching over 30 kpc from the galaxy, tracing ongoing ram pressure stripping as it falls into the Norma galaxy cluster.
2) Analysis of the gas kinematics and stellar velocity field show that ram pressure has removed the interstellar medium from the outer disk while the primary tail is still fed by gas from the galaxy center.
3) The stripped gas retains evidence of the disk's rotational velocity out to 20 kpc downstream, indicating the galaxy is moving radially through the cluster. Beyond this the gas shows greater turbulence,
This document discusses a study that used difference imaging techniques to search for variable stars and microlensing events in the elliptical galaxy Centaurus A. The study obtained deep photometric data over almost two months using the Wide Field Imager on the ESO/MPG 2.2 m telescope. It detected 271 variable stars in Centaurus A with a detection limit of magnitude 24.5. Based on a simple model of Centaurus A's halo, the study estimated it could detect around 4 microlensing events per year, but a higher sensitivity is needed for a meaningful microlensing survey. The spatial distribution of any microlensing events could help constrain the shape of Centaurus A's dark matter halo.
Dust in the_polar_region_as_a_major_contributor_to_the_infrared_emission_of_a...Sérgio Sacani
The mid-infrared emission of the active galactic nucleus NGC 3783 was observed using interferometry over multiple epochs, providing dense coverage of position angles and baselines. The emission was found to be strongly elongated along a position angle of -52 degrees, closely aligned with the polar axis orientation of -45 degrees. The half-light radii were measured to be 20.0 mas by 6.7 mas, corresponding to an axis ratio of 3:1. This implies that 60-90% of the 8-13 micron emission is from the polar-elongated component. The observations support a scenario where the majority of mid-infrared emission in Seyfert galaxies originates from a dusty wind in the polar region,
M82 X-2 is the first pulsating ultraluminous X-ray source discovered. The luminosity of these extreme pulsars, if
isotropic, implies an extreme mass transfer rate. An alternative is to assume a much lower mass transfer rate, but
with an apparent luminosity boosted by geometrical beaming. Only an independent measurement of the mass
transfer rate can help discriminate between these two scenarios. In this paper, we follow the orbit of the neutron star
for 7 yr, measure the decay of the orbit (P P orb orb 8 10 yr 6 1 · » - - - ), and argue that this orbital decay is driven by
extreme mass transfer of more than 150 times the mass transfer limit set by the Eddington luminosity. If this is true,
the mass available to the accretor is more than enough to justify its luminosity, with no need for beaming. This also
strongly favors models where the accretor is a highly magnetized neutron star.
A weak lensing_mass_reconstruction_of _the_large_scale_filament_massive_galax...Sérgio Sacani
This study reports the first weak-lensing detection of a large-scale filament funneling matter onto the core of the massive galaxy cluster MACSJ0717.5+3745. The analysis is based on Hubble Space Telescope images covering an area of 10x20 arcmin^2 around the cluster. A weak-lensing mass reconstruction detects the filament within 3 sigma and measures its projected length as ~4.5 h^-1 Mpc and mean density as (2.92±0.66)×10^8 h74 M⊙ kpc^-2. Assuming constraints on the filament's geometry based on galaxy velocities, the three-dimensional length is estimated to be 18 h^-1 M
Solving the Multimessenger Puzzle of the AGN-starburst Composite Galaxy NGC 1068Sérgio Sacani
Multiwavelength observations indicate that some starburst galaxies show a dominant nonthermal contribution from
their central region. These active galactic nuclei (AGN)-starburst composites are of special interest, as both
phenomena on their own are potential sources of highly energetic cosmic rays and associated γ-ray and neutrino
emission. In this work, a homogeneous, steady-state two-zone multimessenger model of the nonthermal emission
from the AGN corona as well as the circumnuclear starburst region is developed and subsequently applied to the
case of NGC 1068, which has recently shown some first indications of high-energy neutrino emission. Here, we
show that the entire spectrum of multimessenger data—from radio to γ-rays including the neutrino constraint—can
be described very well if both, starburst and AGN corona, are taken into account. Using only a single emission
region is not sufficient.
This document examines whether galaxy environments and the color-density relation can be robustly measured using photometric redshift (photo-z) surveys. It finds that:
1) Using optimized parameters for density measurements, a correlation between 2D projected density measurements from photo-z surveys and true 3D density can still be revealed, even with photo-z uncertainties up to 0.06.
2) The color-density relation remains visible in photo-z surveys out to z=0.8, despite photo-z uncertainties of 0.02-0.06.
3) A deep (i=25 magnitude) photo-z survey with photo-z uncertainties of 0.02 can measure small-scale galaxy
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.
1. This document describes a multiwavelength campaign on the Seyfert 1 galaxy Mrk 509 using five satellites and two ground-based facilities.
2. The campaign aims to study several open questions about active galactic nuclei (AGN), including the location and physics of outflows from AGN, the nature of continuum emission, the geometry and physical state of the X-ray broad emission line region, and the Fe-K line complex.
3. The observations cover more than five decades in frequency, from 2 μm to 200 keV, and include a simultaneous set of deep XMM-Newton and INTEGRAL observations over seven weeks. This allows the authors to disentangle different components and study time variability
ALMA Measurement of 10 kpc-scale Lensing Power Spectra towards the Lensed Qua...Sérgio Sacani
The lensing power spectra for gravitational potential, astrometric shift, and convergence perturbations are powerful probes to investigate dark matter structures on small
scales. We report the first lower and upper bounds of these lensing power spectra on
angular scale ∼ 1
′′ towards the anomalous quadruply lensed quasar MG J0414+0534
at a redshift z = 2.639. To obtain the spectra, we conducted observations of
MG J0414+0534 using the Atacama Large Millimeter/submillimeter Array (ALMA)
with high angular resolution (0.
′′02-0.
′′05). We developed a new partially non-parametric
method in which Fourier coefficients of potential perturbation are adjusted to minimize
the difference between linear combinations of weighted mean de-lensed images. Using
positions of radio jet components, extended dust emission on scales > 1 kpc, and midinfrared flux ratios, the range of measured convergence, astrometric shift, and potential
powers at an angular scale of ∼ 1.
′′1 (corresponding to an angular wave number of
l = 1.2 × 106 or ∼ 9 kpc in the primary lens plane) within 1 σ are ∆κ = 0.021 − 0.028,
∆α = 7 − 9 mas, and ∆ψ = 1.2 − 1.6 mas2
, respectively. Our result is consistent with
the predicted abundance of halos in the line of sight and subhalos in cold dark matter
models. Our partially non-parametric lens models suggest a presence of a clump in
the vicinity of object Y, a possible dusty dwarf galaxy and some small clumps in the
vicinity of other lensed quadruple images. Although much fainter than the previous
report, we detected weak continuum emission possibly from object Y with a peak flux
of ∼ 100 µJy beam−1
at the ∼ 4 σ level.
Keck Integral-field Spectroscopy of M87 Reveals an Intrinsically Triaxial Gal...Sérgio Sacani
The three-dimensional intrinsic shape of a galaxy and the mass of the central supermassive black hole provide key
insight into the galaxy’s growth history over cosmic time. Standard assumptions of a spherical or axisymmetric
shape can be simplistic and can bias the black hole mass inferred from the motions of stars within a galaxy. Here,
we present spatially resolved stellar kinematics of M87 over a two-dimensional 250″ × 300″ contiguous field
covering a radial range of 50 pc–12 kpc from integral-field spectroscopic observations at the Keck II Telescope.
From about 5 kpc and outward, we detect a prominent 25 km s−1 rotational pattern, in which the kinematic axis
(connecting the maximal receding and approaching velocities) is 40° misaligned with the photometric major axis of
M87. The rotational amplitude and misalignment angle both decrease in the inner 5 kpc. Such misaligned and
twisted velocity fields are a hallmark of triaxiality, indicating that M87 is not an axisymmetrically shaped galaxy.
Triaxial Schwarzschild orbit modeling with more than 4000 observational constraints enabled us to determine
simultaneously the shape and mass parameters. The models incorporate a radially declining profile for the stellar
mass-to-light ratio suggested by stellar population studies. We find that M87 is strongly triaxial, with ratios of
p = 0.845 for the middle-to-long principal axes and q = 0.722 for the short-to-long principal axes, and determine
the black hole mass to be ( - ´) 5.37 0.22 10 +
0.25
0.37 9M , where the second error indicates the systematic uncertainty
associated with the distance to M87.
The Population of the Galactic Center Filaments: Position Angle Distribution ...Sérgio Sacani
This document analyzes the position angle (PA) distribution of filaments observed in radio images of the Galactic center, obtained using the MeerKAT radio telescope. It finds that short filaments (<66") have PAs concentrated along the Galactic plane (60-120 degrees), pointing radially towards the supermassive black hole Sgr A*. This suggests the filaments have been aligned by a collimated outflow from Sgr A* extending along the Galactic plane. The outflow pressure is estimated to require an outflow rate of 10^-4 solar masses per year over ~6 million years to align the filaments. Longer filaments (>66") show a broader PA distribution, with a peak around -3 degrees
This project uses computer simulations to model observations of the 2005 Deep Impact collision with comet Tempel 1. The simulations aim to understand the physics behind the light curves observed by Hubble Space Telescope. The simulations suggest the optically thick ejecta cloud was about 28 km in diameter 13 minutes after impact and expanding at around 36 m/s, constraining the cloud's mass to approximately 2x10^7 kg. This mass and expansion velocity are consistent with independent estimates from observations by different astronomy groups.
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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Ähnlich wie 3D-Spatiotemporal forecasting the expansion of supernova shells using deep learning towards high-resolution galaxy simulations
Locating Hidden Exoplanets in ALMA Data Using Machine LearningSérgio Sacani
Exoplanets in protoplanetary disks cause localized deviations from Keplerian velocity in channel
maps of molecular line emission. Current methods of characterizing these deviations are time consuming, and there is no unified standard approach. We demonstrate that machine learning can quickly
and accurately detect the presence of planets. We train our model on synthetic images generated from
simulations and apply it to real observations to identify forming planets in real systems. Machine
learning methods, based on computer vision, are not only capable of correctly identifying the presence
of one or more planets, but they can also correctly constrain the location of those planets.
The first X-ray look at SMSS J114447.77-430859.3: the most luminous quasar in...Sérgio Sacani
SMSS J114447.77-430859.3 (z = 0.83) has been identified in the SkyMapper Southern Survey as the most luminous quasar in
the last ∼ 9 Gyr . In this paper, we report on the eROSITA/Spectrum–Roentgen–Gamma (SRG) observations of the source from
the eROSITA All Sky Survey, along with presenting results from recent monitoring performed using Swift, XMM-Newton, and
NuSTAR. The source shows a clear variability by factors of ∼10 and ∼2.7 overtime-scales of a year and of a few days,respectively.
When fit with an absorbed power law plus high-energy cutoff, the X-ray spectra reveal a = 2.2 ± 0.2 and Ecut = 23+26
−5 keV
. Assuming Comptonization, we estimate a coronal optical depth and electron temperature of τ = 2.5 − 5.3 (5.2 − 8) and
kT = 8 − 18 (7.5 − 14) keV , respectively, for a slab (spherical) geometry. The broadband SED is successfully modelled by
assuming either a standard accretion disc illuminated by a central X-ray source, or a thin disc with a slim disc emissivity profile.
The former model results in a black hole mass estimate of the order of 1010 M , slightly higher than prior optical estimates;
meanwhile, the latter model suggests a lower mass. Both models suggest sub-Eddington accretion when assuming a spinning
black hole, and a compact (∼ 10 rg ) X-ray corona. The measured intrinsic column density and the Eddington ratio strongly
suggest the presence of an outflow driven by radiation pressure. This is also supported by variation of absorption by an order of
magnitude over the period of ∼ 900 d .
Identification of Superclusters and Their Properties in the Sloan Digital Sky...Sérgio Sacani
Superclusters are the largest massive structures in the cosmic web, on tens to hundreds of megaparsec scales. They
are the largest assembly of galaxy clusters in the Universe. Apart from a few detailed studies of such structures,
their evolutionary mechanism is still an open question. In order to address and answer the relevant questions, a
statistically significant, large catalog of superclusters covering a wide range of redshifts and sky areas is essential.
Here, we present a large catalog of 662 superclusters identified using a modified friends-of-friends algorithm
applied on the WHL (Wen–Han–Liu) cluster catalog within a redshift range of 0.05 z 0.42. We name the most
massive supercluster at z ∼ 0.25 as the Einasto Supercluster. We find that the median mass of superclusters is
∼5.8 × 10 15 Me and the median size ∼65 Mpc. We find that the supercluster environment slightly affects the
growth of clusters. We compare the properties of the observed superclusters with the mock superclusters extracted
from the Horizon Run 4 cosmological simulation. The properties of the superclusters in the mocks and
observations are in broad agreement. We find that the density contrast of a supercluster is correlated with its
maximum extent with a power-law index, α ∼ −2. The phase-space distribution of mock superclusters shows that,
on average, ∼90% of part of a supercluster has a gravitational influence on its constituents. We also show the mock
halos’ average number density and peculiar velocity profiles in and around the superclusters.
This document summarizes the results of an MHD simulation coupled with a radiation transport model to simulate X-ray spectra from an accreting black hole. Key points:
- For the first time, the simulation is able to reproduce the main components seen in observed X-ray spectra, including a thermal peak, power-law tail, reflection hump, and iron line, by varying only the mass accretion rate.
- The temperature in the corona varies from 10 keV near the disk to over 100 keV in low-density regions, producing the hard X-ray emission through inverse-Compton scattering.
- Even as the disk's reflection edge varies from the horizon out to 6 gravitational radii with decreasing accretion
Continuum emission from within the plunging region of black hole discsSérgio Sacani
The thermal continuum emission observed from accreting black holes across X-ray bands has the potential to be leveraged as a
powerful probe of the mass and spin of the central black hole. The vast majority of existing ‘continuum fitting’ models neglect
emission sourced at and within the innermost stable circular orbit (ISCO) of the black hole. Numerical simulations, however,
find non-zero emission sourced from these regions. In this work, we extend existing techniques by including the emission
sourced from within the plunging region, utilizing new analytical models that reproduce the properties of numerical accretion
simulations. We show that in general the neglected intra-ISCO emission produces a hot-and-small quasi-blackbody component,
but can also produce a weak power-law tail for more extreme parameter regions. A similar hot-and-small blackbody component
has been added in by hand in an ad hoc manner to previous analyses of X-ray binary spectra. We show that the X-ray spectrum
of MAXI J1820+070 in a soft-state outburst is extremely well described by a full Kerr black hole disc, while conventional
models that neglect intra-ISCO emission are unable to reproduce the data. We believe this represents the first robust detection of
intra-ISCO emission in the literature, and allows additional constraints to be placed on the MAXI J1820 + 070 black hole spin
which must be low a• < 0.5 to allow a detectable intra-ISCO region. Emission from within the ISCO is the dominant emission
component in the MAXI J1820 + 070 spectrum between 6 and 10 keV, highlighting the necessity of including this region. Our
continuum fitting model is made publicly available.
Large scale mass_distribution_in_the_illustris_simulationSérgio Sacani
Observations at low redshifts thus far fail to account for all of the baryons expected in the
Universe according to cosmological constraints. A large fraction of the baryons presumably
resides in a thin and warm–hot medium between the galaxies, where they are difficult to observe
due to their low densities and high temperatures. Cosmological simulations of structure
formation can be used to verify this picture and provide quantitative predictions for the distribution
of mass in different large-scale structure components. Here we study the distribution
of baryons and dark matter at different epochs using data from the Illustris simulation. We
identify regions of different dark matter density with the primary constituents of large-scale
structure, allowing us to measure mass and volume of haloes, filaments and voids. At redshift
zero, we find that 49 per cent of the dark matter and 23 per cent of the baryons are within
haloes more massive than the resolution limit of 2 × 108 M⊙. The filaments of the cosmic
web host a further 45 per cent of the dark matter and 46 per cent of the baryons. The remaining
31 per cent of the baryons reside in voids. The majority of these baryons have been transported
there through active galactic nuclei feedback. We note that the feedback model of Illustris
is too strong for heavy haloes, therefore it is likely that we are overestimating this amount.
Categorizing the baryons according to their density and temperature, we find that 17.8 per cent
of them are in a condensed state, 21.6 per cent are present as cold, diffuse gas, and 53.9 per cent
are found in the state of a warm–hot intergalactic medium.
MUSE sneaks a peek at extreme ram-pressure stripping events. I. A kinematic s...Sérgio Sacani
- MUSE observations of the galaxy ESO137-001 reveal an extended gaseous tail over 30 kpc long traced by H-alpha emission, providing evidence of an extreme ram pressure stripping event as the galaxy falls into the massive Norma galaxy cluster.
- Analysis of the H-alpha kinematics and stellar velocity field show that ram pressure has removed the interstellar medium from the outer disk while the primary tail is still fed by gas from the galaxy center, with gravitational interactions not appearing to be the main mechanism of gas removal.
- The stripped gas retains evidence of the disk's rotational velocity out to around 20 kpc downstream, indicating the galaxy is moving radially along the plane of the sky, while
This document describes observations of the galaxy ESO137-001 using the MUSE instrument on the VLT. The key points are:
1) MUSE observations reveal an extended gas tail stretching over 30 kpc from the galaxy, tracing ongoing ram pressure stripping as it falls into the Norma galaxy cluster.
2) Analysis of the gas kinematics and stellar velocity field show that ram pressure has removed the interstellar medium from the outer disk while the primary tail is still fed by gas from the galaxy center.
3) The stripped gas retains evidence of the disk's rotational velocity out to 20 kpc downstream, indicating the galaxy is moving radially through the cluster. Beyond this the gas shows greater turbulence,
This document discusses a study that used difference imaging techniques to search for variable stars and microlensing events in the elliptical galaxy Centaurus A. The study obtained deep photometric data over almost two months using the Wide Field Imager on the ESO/MPG 2.2 m telescope. It detected 271 variable stars in Centaurus A with a detection limit of magnitude 24.5. Based on a simple model of Centaurus A's halo, the study estimated it could detect around 4 microlensing events per year, but a higher sensitivity is needed for a meaningful microlensing survey. The spatial distribution of any microlensing events could help constrain the shape of Centaurus A's dark matter halo.
Dust in the_polar_region_as_a_major_contributor_to_the_infrared_emission_of_a...Sérgio Sacani
The mid-infrared emission of the active galactic nucleus NGC 3783 was observed using interferometry over multiple epochs, providing dense coverage of position angles and baselines. The emission was found to be strongly elongated along a position angle of -52 degrees, closely aligned with the polar axis orientation of -45 degrees. The half-light radii were measured to be 20.0 mas by 6.7 mas, corresponding to an axis ratio of 3:1. This implies that 60-90% of the 8-13 micron emission is from the polar-elongated component. The observations support a scenario where the majority of mid-infrared emission in Seyfert galaxies originates from a dusty wind in the polar region,
M82 X-2 is the first pulsating ultraluminous X-ray source discovered. The luminosity of these extreme pulsars, if
isotropic, implies an extreme mass transfer rate. An alternative is to assume a much lower mass transfer rate, but
with an apparent luminosity boosted by geometrical beaming. Only an independent measurement of the mass
transfer rate can help discriminate between these two scenarios. In this paper, we follow the orbit of the neutron star
for 7 yr, measure the decay of the orbit (P P orb orb 8 10 yr 6 1 · » - - - ), and argue that this orbital decay is driven by
extreme mass transfer of more than 150 times the mass transfer limit set by the Eddington luminosity. If this is true,
the mass available to the accretor is more than enough to justify its luminosity, with no need for beaming. This also
strongly favors models where the accretor is a highly magnetized neutron star.
A weak lensing_mass_reconstruction_of _the_large_scale_filament_massive_galax...Sérgio Sacani
This study reports the first weak-lensing detection of a large-scale filament funneling matter onto the core of the massive galaxy cluster MACSJ0717.5+3745. The analysis is based on Hubble Space Telescope images covering an area of 10x20 arcmin^2 around the cluster. A weak-lensing mass reconstruction detects the filament within 3 sigma and measures its projected length as ~4.5 h^-1 Mpc and mean density as (2.92±0.66)×10^8 h74 M⊙ kpc^-2. Assuming constraints on the filament's geometry based on galaxy velocities, the three-dimensional length is estimated to be 18 h^-1 M
Solving the Multimessenger Puzzle of the AGN-starburst Composite Galaxy NGC 1068Sérgio Sacani
Multiwavelength observations indicate that some starburst galaxies show a dominant nonthermal contribution from
their central region. These active galactic nuclei (AGN)-starburst composites are of special interest, as both
phenomena on their own are potential sources of highly energetic cosmic rays and associated γ-ray and neutrino
emission. In this work, a homogeneous, steady-state two-zone multimessenger model of the nonthermal emission
from the AGN corona as well as the circumnuclear starburst region is developed and subsequently applied to the
case of NGC 1068, which has recently shown some first indications of high-energy neutrino emission. Here, we
show that the entire spectrum of multimessenger data—from radio to γ-rays including the neutrino constraint—can
be described very well if both, starburst and AGN corona, are taken into account. Using only a single emission
region is not sufficient.
This document examines whether galaxy environments and the color-density relation can be robustly measured using photometric redshift (photo-z) surveys. It finds that:
1) Using optimized parameters for density measurements, a correlation between 2D projected density measurements from photo-z surveys and true 3D density can still be revealed, even with photo-z uncertainties up to 0.06.
2) The color-density relation remains visible in photo-z surveys out to z=0.8, despite photo-z uncertainties of 0.02-0.06.
3) A deep (i=25 magnitude) photo-z survey with photo-z uncertainties of 0.02 can measure small-scale galaxy
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.
1. This document describes a multiwavelength campaign on the Seyfert 1 galaxy Mrk 509 using five satellites and two ground-based facilities.
2. The campaign aims to study several open questions about active galactic nuclei (AGN), including the location and physics of outflows from AGN, the nature of continuum emission, the geometry and physical state of the X-ray broad emission line region, and the Fe-K line complex.
3. The observations cover more than five decades in frequency, from 2 μm to 200 keV, and include a simultaneous set of deep XMM-Newton and INTEGRAL observations over seven weeks. This allows the authors to disentangle different components and study time variability
ALMA Measurement of 10 kpc-scale Lensing Power Spectra towards the Lensed Qua...Sérgio Sacani
The lensing power spectra for gravitational potential, astrometric shift, and convergence perturbations are powerful probes to investigate dark matter structures on small
scales. We report the first lower and upper bounds of these lensing power spectra on
angular scale ∼ 1
′′ towards the anomalous quadruply lensed quasar MG J0414+0534
at a redshift z = 2.639. To obtain the spectra, we conducted observations of
MG J0414+0534 using the Atacama Large Millimeter/submillimeter Array (ALMA)
with high angular resolution (0.
′′02-0.
′′05). We developed a new partially non-parametric
method in which Fourier coefficients of potential perturbation are adjusted to minimize
the difference between linear combinations of weighted mean de-lensed images. Using
positions of radio jet components, extended dust emission on scales > 1 kpc, and midinfrared flux ratios, the range of measured convergence, astrometric shift, and potential
powers at an angular scale of ∼ 1.
′′1 (corresponding to an angular wave number of
l = 1.2 × 106 or ∼ 9 kpc in the primary lens plane) within 1 σ are ∆κ = 0.021 − 0.028,
∆α = 7 − 9 mas, and ∆ψ = 1.2 − 1.6 mas2
, respectively. Our result is consistent with
the predicted abundance of halos in the line of sight and subhalos in cold dark matter
models. Our partially non-parametric lens models suggest a presence of a clump in
the vicinity of object Y, a possible dusty dwarf galaxy and some small clumps in the
vicinity of other lensed quadruple images. Although much fainter than the previous
report, we detected weak continuum emission possibly from object Y with a peak flux
of ∼ 100 µJy beam−1
at the ∼ 4 σ level.
Keck Integral-field Spectroscopy of M87 Reveals an Intrinsically Triaxial Gal...Sérgio Sacani
The three-dimensional intrinsic shape of a galaxy and the mass of the central supermassive black hole provide key
insight into the galaxy’s growth history over cosmic time. Standard assumptions of a spherical or axisymmetric
shape can be simplistic and can bias the black hole mass inferred from the motions of stars within a galaxy. Here,
we present spatially resolved stellar kinematics of M87 over a two-dimensional 250″ × 300″ contiguous field
covering a radial range of 50 pc–12 kpc from integral-field spectroscopic observations at the Keck II Telescope.
From about 5 kpc and outward, we detect a prominent 25 km s−1 rotational pattern, in which the kinematic axis
(connecting the maximal receding and approaching velocities) is 40° misaligned with the photometric major axis of
M87. The rotational amplitude and misalignment angle both decrease in the inner 5 kpc. Such misaligned and
twisted velocity fields are a hallmark of triaxiality, indicating that M87 is not an axisymmetrically shaped galaxy.
Triaxial Schwarzschild orbit modeling with more than 4000 observational constraints enabled us to determine
simultaneously the shape and mass parameters. The models incorporate a radially declining profile for the stellar
mass-to-light ratio suggested by stellar population studies. We find that M87 is strongly triaxial, with ratios of
p = 0.845 for the middle-to-long principal axes and q = 0.722 for the short-to-long principal axes, and determine
the black hole mass to be ( - ´) 5.37 0.22 10 +
0.25
0.37 9M , where the second error indicates the systematic uncertainty
associated with the distance to M87.
The Population of the Galactic Center Filaments: Position Angle Distribution ...Sérgio Sacani
This document analyzes the position angle (PA) distribution of filaments observed in radio images of the Galactic center, obtained using the MeerKAT radio telescope. It finds that short filaments (<66") have PAs concentrated along the Galactic plane (60-120 degrees), pointing radially towards the supermassive black hole Sgr A*. This suggests the filaments have been aligned by a collimated outflow from Sgr A* extending along the Galactic plane. The outflow pressure is estimated to require an outflow rate of 10^-4 solar masses per year over ~6 million years to align the filaments. Longer filaments (>66") show a broader PA distribution, with a peak around -3 degrees
This project uses computer simulations to model observations of the 2005 Deep Impact collision with comet Tempel 1. The simulations aim to understand the physics behind the light curves observed by Hubble Space Telescope. The simulations suggest the optically thick ejecta cloud was about 28 km in diameter 13 minutes after impact and expanding at around 36 m/s, constraining the cloud's mass to approximately 2x10^7 kg. This mass and expansion velocity are consistent with independent estimates from observations by different astronomy groups.
Ähnlich wie 3D-Spatiotemporal forecasting the expansion of supernova shells using deep learning towards high-resolution galaxy simulations (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.
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
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.
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.
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.
PPT on Alternate Wetting and Drying 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.
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.
Immersive Learning That Works: Research Grounding and Paths ForwardLeonel Morgado
We will metaverse into the essence of immersive learning, into its three dimensions and conceptual models. This approach encompasses elements from teaching methodologies to social involvement, through organizational concerns and technologies. Challenging the perception of learning as knowledge transfer, we introduce a 'Uses, Practices & Strategies' model operationalized by the 'Immersive Learning Brain' and ‘Immersion Cube’ frameworks. This approach offers a comprehensive guide through the intricacies of immersive educational experiences and spotlighting research frontiers, along the immersion dimensions of system, narrative, and agency. Our discourse extends to stakeholders beyond the academic sphere, addressing the interests of technologists, instructional designers, and policymakers. We span various contexts, from formal education to organizational transformation to the new horizon of an AI-pervasive society. This keynote aims to unite the iLRN community in a collaborative journey towards a future where immersive learning research and practice coalesce, paving the way for innovative educational research and practice landscapes.
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!
Mending Clothing to Support Sustainable Fashion_CIMaR 2024.pdfSelcen Ozturkcan
Ozturkcan, S., Berndt, A., & Angelakis, A. (2024). Mending clothing to support sustainable fashion. Presented at the 31st Annual Conference by the Consortium for International Marketing Research (CIMaR), 10-13 Jun 2024, University of Gävle, Sweden.
ESA/ACT Science Coffee: Diego Blas - Gravitational wave detection with orbita...Advanced-Concepts-Team
Presentation in the Science Coffee of the Advanced Concepts Team of the European Space Agency on the 07.06.2024.
Speaker: Diego Blas (IFAE/ICREA)
Title: Gravitational wave detection with orbital motion of Moon and artificial
Abstract:
In this talk I will describe some recent ideas to find gravitational waves from supermassive black holes or of primordial origin by studying their secular effect on the orbital motion of the Moon or satellites that are laser ranged.
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2. 3D SN-explosion forecast with deep learning 4055
MNRAS 526, 4054–4066 (2023)
of 2 × 109
M in a cosmological simulation to z = 0 and is
able to capture the propagation of SN blast waves. For an isolated
dwarf galaxy simulation, even higher resolutions are achieved:
4 M (Hislop et al. 2022) and ∼1 M (Hu 2019) for the gas
mass. The SImulations Resolving Individual Stars (SIRIUS; Hirai,
Fujii Saitoh 2021) achieves a gas-mass resolution of 18.5 M in
cosmological zoom-in simulations of ultrafaint dwarf galaxies.
Computational issues remain to be addressed to achieve MW-sized
simulations with ∼ 1 M resolution. To conduct such simulations, we
need to use more than 1010
gas and star particles, at least two orders
of magnitude larger than those for the current similar simulations.
One of the most serious bottlenecks is the short time-steps required
for resolving blast waves in dense regions. In recent high-resolution
galaxy simulations, such as the dwarf simulations described above,
individual (hierarchical) time-steps are employed to decrease the
number of redundant calculations. The SN-affected particles, which
comprise a tiny fraction of the entire Galaxy, are integrated using
much shorter time-steps than the rest of the particles, for which
a large and shared time-step (global time-step) can be employed.
However, even with this method, in MW star-by-star simulations,
the problem of communication overhead would still remain; the
data transfer among nodes is required at every smallest time-step,
and a large amount of CPU cores are forced to idle during such
communications.1
One solution to this is to send SN-affected particles
to a separate set of CPUs and integrate small-scale phenomena
separately from the entire system during a global time-step with
techniques such as the Hamiltonian splitting method (Wisdom
Holman 1991; Saha Tremaine 1994; Xu 1995; Springel 2005;
Fujii et al. 2007; Ishiyama, Fukushige Makino 2009; Saitoh
Makino 2010; Pelupessy Portegies Zwart 2012; Jänes, Pelupessy
Portegies Zwart 2014; Rantala, Naab Springel 2021; Springel et al.
2021; Rantala et al. 2022).
Currently, the application of such a splitting method for SN
feedback is not developed because it is difficult to predict the
expansion of the SN shells and to pre-identify the particles that
should be separately computed. The simplest approach is using an
analytic solution for the time evolution of the SN shell in an isotropic
and uniform ISM (Sedov 1959). However, since the ISM of the actual
galactic environment is neither isotropic nor uniform, the SN shell
would expand anisotropically, and this method fails to accurately
predict the expansion regions of the SN shell in galaxy simulations.
We need a more sophisticated method that can capture the complex
expansion.
In this study, we propose to use deep learning to forecast the
expansion of the SN shell. In astronomy, deep learning has been
used to solve many problems. In particular, convolutional neural
networks (CNNs) are commonly used for analysing spatial features
of 2D or 3D data obtained in simulations; 2D CNNs have been used
to emulate the dynamics of baryonic simulations (e.g. Chardin et al.
2019; Duarte, Nemmen Navarro 2022), and 3D CNNs have been
used to increase the resolution of cosmological simulations (e.g. Li
et al. 2021) and emulate turbulent hydrodynamical simulations (Chan
et al. 2022). Recurrent models extract temporal trends in sequential
data and are also used in astronomy. For instance, Lin Wu (2021)
used a recurrent neural network (RNN) to analyse gravitational wave
signals. Combining a CNN and recurrent model will allow us to
1The overhead of communication becomes more dominant and worsens the
scalability as the number of processors and/or steps increases. In recent
particle-based galaxy formation simulations, the scaling saturates on ∼103 −
104 CPU cores (Hopkins et al. 2018; Springel et al. 2021).
analyse the time series of spatial distribution data obtained in a
simulation. In this study, we develop a deep learning model composed
of 3D CNNs and recurrent modules to predict the 3D expansion of
SN shells in inhomogeneous ISM.
We study deep learning forecasts of SN shells in dense regions
0.1 Myr after the explosion. In this paper, we will show that our
model can predict the evolution of SN shells, which contain SN
particles inside, in the turbulent ISM with gravity and radiative
cooling and heading. The paper is organized as follows. In Section 2,
we explain the set-up of our SN simulations and the data preparation
methodology. We describe the models to the SN shells in Section 3,
where Section 3.1 lays down the analytic solution and Section 3.2
provides our new deep learning model. In Section 4, we present
the results of forecasting the expansion of SN shells using our
deep learning model and evaluate the generalization performance.
In Section 5, we discuss practical implementations of our new model
in future galaxy simulations. Section 5.1 demonstrates how our
approach can be utilized to detect SN-affected particles. Section 5.2
also explores potential ways to integrate our model into upcoming
simulations of galaxies. Finally, Section 6 summarizes the paper and
discusses the potential extension of our model and implementation
of our future high-resolution Galaxy simulations.
2 DATA PREPARATION
We prepare training data from smoothed particle hydrodynamics
(SPH) simulations of an SN explosion inside the inhomogeneous
density distribution of molecular cloud for deep learning. The
resolution of these simulations is adjusted to our upcoming star-
by-star Galaxy simulations.
2.1 Code
We simulate SN explosions using our N-body/SPH codes, ASURA-
FDPS (Saitoh et al. 2008; Iwasawa et al. 2016) and ASURA + BRIDGE
(Fujii et al. 2021). In these codes, hydrodynamics are calculated using
the density-independent SPH (DISPH) method (Saitoh Makino
2013, 2016), which can properly estimate the density and pressure
at the contact discontinuity and reproduce fluid instabilities. The gas
properties are smoothed using the Wendland C4
kernel (Dehnen
Aly 2012). The kernel size is set to keep the number of neighbour
particles at 125 ± 1. We adopt the shared time-steps with the
Courant-like hydrodynamical time-step based on the signal velocity
(Monaghan 1997; Springel 2005). The leap-frog method is used for
time integration. The time-step of a particle i is written as
ti = CCFL
2hi
maxj[ci + cj − 3wij]
, (1)
where CCFL = 0.3, hi and ci are the SPH kernel length and sound
speed of a particle i, and
wij = vij · rij/rij, (2)
where rij and vij are the relative position and velocity between
particles i and j, respectively. The index j runs over all the particles
within the kernel size from the particle i. The time-step for integration
t is then determined as
t = min
i
ti. (3)
We adopt the artificial viscosity term originally introduced by
Monaghan (1997). The time-dependent variable viscosity parameter
form proposed by Rosswog (2009) is also used. The range of
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Figure 1. Snapshots of our SN simulation of density distribution for the Fiducial data. Figures show the time variation of density after an SN explosion until
0.133 Myr.
the viscosity parameter is 0.1–3.0 in our simulations. We use the
metallicity dependent cooling and heating functions from 10 to 109
K generated by CLOUDY version 13.5 (Ferland et al. 1998, 2013,
2017). Assuming the environment of the MW Galaxy, metallicity of
Z = 1 Z is adopted in our runs.
2.2 Supernova simulation set-up
We design the simulations as an SN explosion in a high-density star-
forming molecular cloud with a large density contrast. We assume
an adiabatic compression of a monatomic ideal gas, which follows
the equation of state with the specific heat ratio γ = 5/3:
P = (γ − 1)ρu, (4)
where P, ρ, and u are the pressure, smoothed density, and specific
internal energy, respectively. The adiabatic compressible gas clouds
follow the following equations:
dρ
dt
= −ρ∇ · v, (5)
d2
r
dt2
= −∇P
ρ
+ avisc − ∇, (6)
du
dt
= −P
ρ
∇ · v + −
ρ
, (7)
where r is the position, avisc is the acceleration generated by the
viscosity, is the gravitational potential, is the radiative heat
influx per unit volume, and is the radiative heat outflux per unit
volume.
The process of the SN simulations is as follows. First, to make gas
clouds similar to star-forming regions, we evolve initially uniform-
density gas spheres with a turbulent velocity field that follows ∝ v−4
for one initial free-fall time. As for the initial gas sphere of the
fiducial data set, a total mass of 106
M, a radius of 60 pc, and a
uniform density of 190 cm−3
are adopted. The initial conditions are
constructed using the Astrophysical Multi-purpose Software Envi-
ronment (Pelupessy et al. 2013; Portegies Zwart et al. 2013; Portegies
Zwart McMillan 2018). We use SPH particles with a mass of 1
M and an initial temperature of 100 K. These parameters are chosen
to be comparable to the galaxy simulations we aim to perform. We
confirm that the mass resolution of our SN simulations is sufficient
to reproduce the blast wave properties of SNe by performing the
Sedov blast wave test (Sedov 1959; Saitoh Makino 2013; see
Appendix A). The softening length for gravitational interactions is
set to 0.9 pc.
Then, the thermal energy of 1051
erg is injected into 100 SPH par-
ticles in the centre of the turbulent gas clouds as the explosion energy.
The thermal energy is distributed to the particles by smoothing with
a SPH kernel. SNe happen at the centre of the turbulent gas clouds in
the simulations. The simulations of an SN explosion are performed
for up to 0.2 Myr from the beginning of the energy injection. The
upper panels of Fig. 1 show an example of the evolution of the gas
density distribution after a SN explosion.
We also conduct simulations with a shorter duration and denser
initial conditions. In addition, we consider two extra cases with
different mean densities where there is no density fluctuation. All
these simulations were used to generate training and test data sets.
The data set names and parameters are summarized in Table 1. Our
simulations were performed using the supercomputer Cray XC50
at the Center for Computational Astrophysics (CfCA), National
Astronomical Observatory of Japan.
2.3 Training data for deep learning
For deep learning, we extract the central cubic regions with a side
length of 60 pc and obtained 3D volume images composed of 323
voxels with a spatial resolution of 1.9 pc by smoothing gas particles
with SPH kernels of size depending on the local densities. The SNe
are placed at the centre of the 3D volume images. The extracted
regions are small enough compared to the turbulent clouds, and the
boundary effects can be ignored. We performed 300 independent
simulations of SN explosions with different seeds for the turbulence
velocity fields and got 20 snapshots with a time-step t. The initial
turbulent gas clouds for the Fiducial training data sets have mean
densities ranging from 4.1 × 10 to 6.5 × 10 cm−3
. The average and
standard deviation of the mean densities are 5.4 × 10 and 4.0 cm−3
,
respectively. In training, the densities are normalized by 1.9 × 102
cm−3
so that the majority of the data values fall within the range of
0 to 1.
We prepare two training data sets with different time-steps as listed
in Table 1: t = 7.0 × 10−3
Myr (Fiducial) and t = 3.5 × 10−3
Myr (Short-term data set). A sequence of data converted from each
simulation contains 20 volume images. We call a volume image in a
sequence, a frame.
To augment training data, flipped volume images and images with
swapped axes (transposition) are added to the training data. There are
23
= 8 possible combinations of axes to flip and 3! = 6 combinations
of axes to swap. We thus generate 48(= 8 × 6) data sequences for
each of the 300 simulations.
3 METHODS TO PREDICT SN SHELL
EXPLOSION
3.1 Analytic solution of the expansion of SN shell
The expansion of the SN shell is described as a self-similar solution
known as the Sedov–Taylor solution (Sedov 1959). This solution
approximates the SN as a spherical point explosion in a uniform
medium. Introducing the dimensionless similarity variable ξ, the
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Table 1. The simulation properties (i.e. the average density ρ̄, spatial symmetries of
gas clouds, and the forecast horizon t) of the data sets used for training and testing
our deep learning models. We have four data sets: Fiducial, Short-term, Uniform, and
Dense-uniform. We use the Fiducial and Short-term data sets to train deep learning
models. The combinations of data sets used for training and testing are shown in
Table 2.
Data sets ρ [cm−3] Spatial symmetries t [Myr]
Fiducial 4.1 × 10 − 6.5 × 10 Non-uniform and
anisotropic
0.133
Short-term 4.1 × 10 − 6.5 × 10 Non-uniform and
anisotropic
0.066
Uniform 5.6 × 10 Uniform and isotropic 0.133
Dense-uniform 1.9 × 102 Uniform and isotropic 0.133
time evolution of the radius of the SN shell is written as
R(t) = ξ
E
ρ
1/5
t2/5
, (8)
where E and ρ are the energy injected by SN and the density of the
surrounding ISM, respectively. Equation (8) is the analytic solution
that can be used under the ideal environment of uniform density.
However, the interstellar gas is not uniform, and therefore this
equation is not always applicable for predicting SN shell evolution.
We thus need to develop a model for non-uniform environments.
3.2 Prediction for the SN explosion
Several deep learning techniques for video prediction have been
developed in the past several years. In particular, deep learning
models combining CNNs and RNNs, which learn spatial correlations
in images and temporal correlations in time series, are often used (for
review, Oprea et al. 2020). To forecast the time series data of the SN
explosion, we develop such a combined model based on MEMORY IN
MEMORY (MIM) NETWORK2
developed by Wang et al. (2018).
The schematic diagram of our model is shown in Fig. 2. The model
predicts 3D gas density distributions at a time-step ti (i = 1, 2, ...,
20) from those at the previous time-step ti − 1, where ti − ti − 1 =
t. We denote the simulated and predicted density distributions at
time t as x(t) and y(t), respectively. The input data are either x(t0)
or y(ti) (i = 1, 2, ..., 19). By repeating the next-time-step predictions
20 times from t0 = 0, we forecast the gas density distribution at t20 =
20t.
Our model has three MIM blocks with two recurrent modules
with convolutional operations. In each module in the MIM block,
the input data are convolved with a set of 3D data cubes called
memory cells. The memory cells are initialized at the first prediction
and are updated at each prediction, storing the information on the
time variation of the gas distribution over all previous time-steps.
We initialize the memory cells with a uniform distribution. The
two modules are designed differently to capture stationary and non-
stationary variations in data, respectively, allowing the model to learn
complex, non-stationary evolution of SN explosions more efficiently
than conventional methods.3
See Wang et al. (2018) for more details
on the inner architecture of the modules.
2https://github.com/Yunbo426/MIM
3Traditional time-series forecasting models have been developed for station-
ary time series, which have a constant mean and autocovariance over time
(for review, Wilson 2016). In such models, non-stationary time series is
transformed into stationary data in some ways (e.g. linear and logarithmic
transformations) and then predicted. However, high-order non-stationarity
Our new implementation for the original MIM network is the
following two points. First, we increase the internal dimension of the
model by 1, from 2D to 3D, to deal with the 3D density distribution.
Second, we change the number of input and output data cubes. The
original MIM network is a many-to-many forecast model predicting
the last ten frames from the initial ten. We design our model as
a one-to-many forecast model that takes an image just before the
SN explosion as an input and returns all the gas distributions of
subsequent time-steps. We call our new forecast model 3D-MIM.4
We implement our model using TensorFlow5
and train it using the
NVIDIA GeForce RTX 3090 GPU installed on the desktop computer
of the corresponding author and the NVIDIA A100. The model
is trained with L2 loss function between the true (simulated) and
predicted gas density distributions for 64 epochs with batch size 4.
We adopt ADAM optimizer (Kingma Ba 2014) with a learning
rate of 0.001. For inference, computationally expensive architectures
in our deep learning models (e.g. 3D-CNNs) are optimized to
the supercomputer Fugaku by SOFTNEURO R
(Hilaga et al. 2021)
developed by Morpho, Inc.
4 RESULT
We show the test results on our 3D-MIM using four different test data
(Table 2). We first use the Fiducial data set for the training and test
data set (Experiment 1; Table 2). The training and test data sets are
generated from different sets of simulations (random seeds). Fig. 3
shows an example of the forecast result using 3D-MIM. Panels (a–
c) of Fig. 3 show the initial distribution, the simulated distribution
(ground truth), and the forecast result at t = 20t = 0.13 Myr,
respectively. The red crosses in the centre represent the position of
the SN explosion.
In panels (b) and (c) of Fig. 3, we show the shell radius in
orange dashed lines. The shell is defined by the boundary of the
regions where the density decreases by more than 10 per cent of the
initial densities for simplicity. For reference, the red dotted circles
represent the shell radius estimated using the analytic solution given
by equation (8). In the simulated result [panel (b)], while the shell
spreads out as much as in the analytic solution on the left, the blast
wave is stopped by a dense filament on the lower right, making the
spread of the shell smaller. A similar trend is also observed in the
predicted result [panel (c)], showing that the 3D-MIM can properly
cannot be captured with such an implementation (see discussion in Wang
et al. 2018).
4https://github.com/kyaFUK/3D-MIM
5https://github.com/tensorflow/tensorflow
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Figure 2. The architecture of our deep learning framework, 3D-MIM, which consists of three MIM blocks. The model predicts 3D gas density distributions
at a time-step ti + 1 from those at the previous time-step ti. An MIM block includes two modules to capture non-stationary and stationary variations, where the
input data are convolved with memory cells. We omit the detailed internal structures of the modules, see Wang et al. (2018) for more details.
Table 2. The settings for experiments. The names of data sets correspond to
those in Table 1. Experiments 1, 2, and 3 use the same trained models.
Experiment Training data Test data
Experiment 1 Fiducial Fiducial
Experiment 2 Fiducial Uniform
Experiment 3 Fiducial Dense-uniform
Experiment 4 Short-term Short-term
reproduce the anisotropic shell propagation. Additional examples of
the prediction are laid on Appendix C.
To confirm the convergence of the training, we compute two
metrics: mean absolute percentage error (MAPE) and mean structural
similarity (MSSIM; Wang et al. 2004) between the simulated
and forecast data. The MAPE measures prediction accuracy for
every predicted voxels and ranges in [0,1]. The MSSIM quantifies
the structural similarity between simulated and predicted density
distribution and ranges in [ −1,1]. The lower value of MAPE and
the higher value of MSSIM indicate that the two images are more
similar. See Appendix B for more details on these metrics. MAPE
and MSSIM are calculated by equations (B1) and (B2), respectively.
Fig. 4 shows these metrics as a function of epochs for Experiment
1, where we use the Fiducial data set for training and testing. Each
colour corresponds to a different frame. We find that these metrics
converge as the number of epochs increases. This suggests that
our model does not suffer from overfitting. It also implies that the
parameters’ weights of the neural network also converge and that
the model does not improve further with continued training. Frame-
by-frame comparisons of these two metrics show that the longer the
forecast period is, the more difficult the reproduction becomes. When
we use other experiments, these metrics as functions of epochs show
a similar tendency (Fig. 5).
To further examine the general performance of our model, the
difference between the radius predicted by the model and the analytic
solution using equation (8) is tested. In this test, we use both
approaches to predict the radius of SN shells in uniform-density
distributions. We note that the model was not trained with such
uniform-density SN explosion simulations. Fig. 6 shows the test
results at 0.1 Myr of Experiment 2 (left) and Experiment 3 (right).
In Experiment 2, we use the same average density as the training
data (5.6 × 10 cm−3
, left), whereas in Experiment 3, we adopt a
higher density (1.9 × 102
cm−3
, right). In both cases, background
gas is uniform and isotropic. In Fig. 6, the red circles show the Sedov
solution calculated using equation (8). The shell (high-density peak)
in the forecast result matches the analytic solution well when the
uniform unit density is input (left), although the model is not trained
with such a uniform distribution. When the ISM with high density
is adopted (right), the estimated shell size is smaller than that of
the ISM with mean density (left). Although the expected density
dependence trend from the analytic solution is accurate, there are
slight discrepancies in the sizes. This difference suggests that the
model has not completely learned the scaling law.
To correctly predict it, we may need to vary the densities in training
data more. Another possibility is to train multiple 3D-MIMs with
different density ranges and choose an appropriate one to apply every
time a SN occurs in simulation. In practice, the average density of
the ambient ISM must be calculated each time, but the computational
cost for this is small enough.
5 DISCUSSION
5.1 Application for the identification of SN-affected particles
So far, we have seen that our model sufficiently predicts the expansion
of SN shells. Such a forecast result could be used for improving future
galaxy simulations.
As discussed in Section 1, one way to address the issues of
communication overhead in galaxy simulations is a Hamiltonian
splitting method. In this method, the Hamiltonian of a system is
split into two parts: short and long time-scales. Particles with short
time-scales (e.g. SN-affected particles) are integrated with short
time-steps, and the force from long time-scale particles is given
as a perturbation in a longer time-step (global time-step; Wisdom
Holman 1991). For future high-resolution galaxy simulations, we
consider splitting the Hamiltonian into terms for the SN-affected
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Figure 3. A forecast result by the 3D-MIM for Experiment 1 in Table 2. Panel (a) the initial distribution just before the SN explosion at the centre. Panel (b)
the simulation result at 0.1Myr after the SN explosion (ground truth). Panel (c) the 3D-MIM’s forecast result at 0.1Myr. Red crosses show the centre of the
explosion. In panels (b) and (c), red dotted circles represent the shell radius estimated by the analytic solution (8). Orange dashed lines show the boundary of
the regions where the densities decrease by more than 10 per cent of the initial densities by the explosion.
One side of each panel corresponds to 60 pc. Colour maps show the density distribution. The colour bar and scale are the same in panels (a–c).
Figure 4. Left: Mean absolute percentage error (MAPE). Right: Mean structural similarity (MSSIM) as functions of the epoch at several frames for Experiment
1. Each colour corresponds to t = 1.4 × 10−2, 4.2 × 10−2, 7.0 × 10−2, 9.8 × 10−2, and 1.26 × 10−1 Myr (frame 2, 6, 10, 14, and 18) after the SN explosion.
The lower value of MAPE and the higher value of MSSIM mean that the two images are more similar.
particles and the others as illustrated in Fig. 7. At every global
time-step, we separately integrate the SN-affected particles using
short time-steps shown in lower panels in Fig. 7. Although those
particles are challenging to analytically detect in advance, they could
be selected using a forecast result by our deep learning model.
We define target particles as those that require smaller time-
steps than the subsequent global timeistep and have a temperature
above 100 K. The temperature threshold is given to exclude star-
forming gas. We call the rest of the particles non-target particles.
In our deep learning model, the central bubbles can be detected by
extracting the regions where the density decreases at a certain level.
As a demonstration, we consider regions with more than 10 per cent
density reduction. By image processing, we then slightly expand the
detected bubble to cover the surrounding shell that also holds target
particles (see Appendix D1).
In comparison to the analytic approach detailed in Appendix D2,
which relies on equation (8), we assess the computer vision approach.
We compute the target identification rate (the ratio of identified
particles to true target particles) and non-target fraction (the ratio
of non-target to target particles inside the forecast region). The
parameters for particle identification are chosen so that we obtain
similar non-target fractions for the analytic solution (8) and our 3D-
MIM.
Fig. 8 shows the results of our approach (blue) and the analytic
approach (orange) for Experiment 1 (Table 2). The identification
rates of our approach are significantly higher than those of the
analytic approach. This is because our deep learning model can
capture anisotropically distributed particles long after the explosion,
whereas the analytic solutions cannot.
In general, there is a trade-off; a very high identification rate
could be obtained if we allow a high non-target fraction. In actual
simulations, the parameters (e.g. criteria) for particle detection
must be selected according to the required selection efficiency. In
particular, we should adopt an identification rate with which the
reproduction of the blast wave can be achieved within the required
accuracy by simply evolving only the selected particles.
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Figure 5. Left: Mean absolute percentage error (MAPE). Right: Mean structural similarity (MSSIM) as functions of the epoch at several frames for Experiment
4. Each colour corresponds to t = 7.0 × 10−3, 2.1 × 10−2, 3.5 × 10−2, 4.9 × 10−2, and 6.1 × 10−2 Myr (frame 2, 6, 10, 14, and 18) after the SN explosion.
Figure 6. The test results of the shell expansion at 0.1 Myr after a SN
explosion with Experiment 2 [panel (a)] and Experiment 3 [panel (b)] in
Table 2. One side of each panel corresponds to 60 pc. The uniform densities
of panels (a) and (b) are equal to and more than the mean density in SN
simulations in training data, respectively.
We note that our model is not trained using the data set of uniform density
distributions but the Fiducial data set in Table 1. Red circles indicate the
expanding shell radius obtained from the Sedov–Taylor solution [equation
(8)].
5.2 Application to galaxy simulations
This section discusses other physical processes that we should
consider in the practical implementation of our model in future galaxy
simulations.
Several events other than SNe would also reduce the required
calculation time-steps in cosmological simulations of the MW-sized
Galaxy. For instance, merging the main haloes and ram pressure-
stripped satellites can generate shock-heated gas that reduces time-
steps. However, their time-steps would not be as small as those for
SNe because the Galactic halo gas is much less dense than that of
disc region (10−5
− 10−3
cm−3
; Bland-Hawthorn Gerhard 2016)
compared to star-forming regions, which we focus on in this paper.
When we apply the Hamiltonian splitting, we should also confirm
that the physical processes other than SN feedback that affect ISM
can be incorporated properly. One of the most important effects is the
far ultraviolet (FUV) radiation, which impacts cooling and heating
(Hu et al. 2017; Hu 2019; Hislop et al. 2022). The heating rate from
FUV photons is proportional to their flux in cold and dense regions
such as star-forming regions (Forbes et al. 2016). The energy density
Figure 7. Upper panels show the galaxy’s spiral arms in a simulation at two
global time-steps, and lower panels display the zoom-in of the arm where an
SN is exploding. In the Hamiltonian splitting method, the particles affected
by SNe are integrated separately from the entire galaxy with a short time-step
and a low parallelization degree. To apply this method, we need to predict
the region where the particles are affected by SNe during the global time-step
(i.e. the region surrounded by the red line) in advance. Image credit: [upper:
NASA/JPL-Caltech/ESO/R. Hurt, lower: ESA/Hubble (L. Calc
¸ada).].
of a gas particle contributed by FUV luminosity u is calculated as
u =
i
Li
4πcr2
i
, (9)
where c, Li, and ri represent the speed of light, FUV luminosity
of a star particle i, and distance between the gas and star particle,
respectively (Hu et al. 2017). For the contribution from outside the
split region (SN-affected region), the radiation can be considered not
to change quickly, and thus the summation in equation (9) can be
executed only at every global time-step, i.e. at the same time as the
gravity tree walking. For the internal radiation, if any, as the self-
shielding is expected to be effective inside dense gas clouds, it would
be sufficient to consider that it only contributes locally, similar to the
treatment in Hu et al. (2017). This way, other physical processes can
still be computed adequately with Hamiltonian splitting methods.
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Figure 8. The comparison of the approach based on the analytic solution
(8) (represented as ‘Analytic’) and our model (represented as ‘3D-MIM’) for
global time-steps of t = 0.1 Myr. The vertical axis indicates the ratio of the
non-target to the target particles inside the forecast region. The horizontal
axis indicates the fraction of target particles we successfully detected. Pairs
of the same symbols indicate the results using the same simulation data.
6 CONCLUSION
We developed a new deep learning model, 3D-MIM, successfully
forecasting the time evolution of the gas density distribution for
0.1 Myr after a SN explosion. To apply for 3D numerical simulations,
the model is expanded from a 2D model originally utilized by
video prediction by increasing the dimensionality. Compared to the
analytic solution, our method has the advantage of predicting the
evolution of non-uniform gas clouds. The performance of the 3D-
MIM was evaluated using the metrics of MAPE and MSSIM for
image reproductions. Additionally, we forecast the shell expansion
of a SN in a uniform density distribution, which was not included in
the training data set. The 3D-MIM successfully reproduced the shell
radius consistent with an analytic solution and demonstrated high
convergence values and generalization capabilities.
Such a method presented in this paper could be used to pre-
identify the SN particles that require short time-steps in large, high-
resolution galaxy formation simulations. By combining this with
the Hamiltonian splitting method, we would be able to integrate
such particles separately from the entire galaxy. In the future study,
we will include our deep learning model and Hamiltonian splitting
method in our N-body/SPH code, ASURA-FDPS (Saitoh et al. 2008;
Iwasawa et al. 2016), to achieve a star-by-star Galaxy formation
simulation. We note that some practical issues still need to be
discussed in more detail, including the required identification rate and
the implementation of other physical processes. We will investigate
them in the future study.
Finally, as an interesting application of our 3D-MIM, we briefly
mention the possibility of replacing the time consuming computation
of SNe with machine prediction, which would require much smaller
computational costs than adopting the splitting scheme we consider
in this paper. We can develop such a machine by designing it to learn
the distributions of all the physical quantities, including velocity
and temperature. Such an attempt at replacement has been actively
studied in recent years (Chan et al. 2022; Duarte et al. 2022), but it has
several technically challenging problems to overcome. For example,
an extreme amount of simulations for training data is necessary
to obtain robust prediction over various physical conditions in a
simulation. It is also required to find appropriate transform functions
for the training data to allow the machine to properly learn the
physical quantities spread over several orders of magnitude (e.g.
Chan et al. 2022). We will also explore the future use of 3D-MIM in
this direction.
ACKNOWLEDGEMENTS
The authors thank an anonymous referee and the referee, Ulrich P.
Steinwandel, for the useful comments on the paper. The authors are
also grateful to Takashi Okamoto for fruitful discussions. Numerical
computations were carried out on Cray XC50 CPU-cluster at the
Center for Computational Astrophysics (CfCA) of the National
Astronomical Observatory of Japan. The model was also trained
using the FUJITSU Server PRIMERGY GX2570 (Wisteria/BDEC-
01) at the Information Technology Center, The University of Tokyo.
This work was also supported by Japan Society for the Promotion of
Science (JSPS) KAKENHI grant numbers 22H01259, 22KJ0157,
20K14532, 21H04499, 21K03614, and 23K03446, Ministry of
Education, Culture, Sports, Science and Technology as ‘Program
for Promoting Researches on the Supercomputer Fugaku’ (Structure
and Evolution of the Universe Unraveled by Fusion of Simulation and
AI; grant number JPMXP1020230406; Toward a unified view of the
universe: from large scale structures to planets), and the University
of Tokyo Excellent Young Researcher Program. KH was financially
supported by JSPS Research Fellowship for Young Scientists and
accompanying grants-in-aid for JSPS Fellows (22J23077), Japan
Educational Exchanges and Services·Mistubishi Corporation Sci-
ence Technology Student Scholarship in 2022, and the Innovation
for Intelligent World programme of The University of Tokyo.
DATA AVAILABILITY
The 3D-MIM is open-source on GitHub at https://github.com/kyaFU
K/3D-MIM. The data supporting this study’s findings are available
from the corresponding author, KH, upon reasonable request.
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APPENDIX A: RESOLUTION STUDY OF
BLASTWAVE TEST
We test the Sedov explosion problem (Sedov 1959) using our DISPH
code (Saitoh Makino 2013, 2016). The parameters for this test
are similar to the point-like explosion tests carried out in Saitoh
Makino (2009). Since this is an idealized test, unlike Section 2.1,
we do not consider self-gravity and radiative cooling/heating. The
equations we use in this test are as follows:
P = (γ − 1)ρu, (A1)
dρ
dt
= −ρ∇ · v, (A2)
d2
r
dt2
= −∇P
ρ
+ avisc, (A3)
du
dt
= −P
ρ
∇ · v. (A4)
As described in Section 3.1, the system of a spherical point
explosion in a uniform media has the dimensionless similarity
variable of the Sedov solution. By transforming equation (8), the
dimensionless similarity variable ξ can be written as
ξ =
ρ0
E0
r
t2/5
, (A5)
where E0, ρ0, r, and t is the injected energy, initial density, radius of
the shell, and elapsed time, respectively. These physical quantities
are normalized to the dimensionless parameter in this test: ρ0 and E0
are normalized to unity. A SN explodes at r = 0 at t = 0, and 643
particles are used.
Fig. A1 shows the simulation result at t = 5.0 × 10−2
for the
dimensionless time. Applying the dimensionless parameters to equa-
tion (A5), the value of the dimensionless similarity valuable ξ = 1.13
Figure A1. The simulation result of the Sedov explosion problem (Sedov
1959). The simulation was performed with the DISPH scheme (Saitoh
Makino 2013, 2016) that is used in our SN simulation code. The result is
scaled to the mean density of 4.1 × 10 cm−3 at t = 104 yr. Red solid curve
is the analytic solution for the radial density profile of the blast wave derived
by Sedov (1959). Blue dotted curve is geometrical means of the density in
the simulation.
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Figure A2. Evolution of a SN remnant in the cold neutral medium (the initial temperature T = 100 K and density n0 = 45 cm−3). Three different mass
resolutions are adopted: mgas = 0.1 (solid), 1 (dotted), and 10 (dashed) M. Panel (a) the linear momentum of the shell; panel (b) the thermal energy (red) and
kinetic energy (blue); panel (c) the shell velocity, defined by the total momentum divided by the shell mass; panel (d) the shell mass. The shell was defined by
all particles, which have the temperature of T 2 × 104 K and the velocity v 0.1 km s−1.
Figure A3. Density profile corresponding to the radius at the elapsed time
at t = 10−2 and t = 10−1 Myr from the energy injection. Line style means
the same as Fig. A2.
is obtained while ξ = 1.15 for the adiabatic gas analytically derived
by Sedov (1959). Using ξ = 1.15, the dimensionless parameters, and
equation (8), the obtained relationship between the radius and density
are scaled to the similar parameters as the sparsest case in our training
data set: the mean density of the ambient gas 4.1 × 10 cm−3
, input
energy 1051
erg, and elapsed time 104
yr (Fig. A1). From this test, the
required mass resolution is obtained as 6.5 M. The mass resolution
mgas = 1 M, chosen in our SN simulations for the training data,
is sufficient. This conclusion is also supported by Steinwandel et al.
(2020). They also detected the blast wave under a similar condition
using SPH with the mass resolution of 1 M (table 1 in Steinwandel
et al. 2020).
We conduct an additional test on the SN feedback in a spherical
gas cloud with a uniform density to confirm the convergence with
the mass resolution. Such tests have also been done in appendix B
in Hu et al. (2016), but here we adopt higher metallicity and include
the gravitational forces to evaluate the convergence in more practical
conditions. We use three different resolutions (mgas = 10, 1, and
0.1 M). The injection masses are Minj = 1000, 100, and 10 M,
respectively. We simulate the evolution of a supernova remnant
(SNR) with the injected energy ESN = 1051
erg in a spherical gas
cloud with a uniform density nH = 45 cm−3
. The ambient gas has the
initial temperature T = 100 K. We refer to the mass of the hot bubble
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(T ≥ 2 × 104
K) and cold shells (T 2 × 104
K) to evaluate the
convergence depending on the resolution following the definition in
Steinwandel et al. (2020). The threshold of velocity v 0.1 km s−1
is also set to distinguish the shell and ambient gas. The gravitational
softening length for gas is set to be 2, 0.9, and 0.5 pc for the SPH
particle mass of 10, 1, and 0.1 M.
Fig. A2 shows the evolution of the SN feedback. The momentum
is overestimated in panel (a) at the worst resolution (10 M). This is
consistent with the results of Steinwandel et al. (2020) although they
consider lower metallicity environments. Since the run with 10 M
resolution does not resolve the thin- and high-density shell (Fig. A3),
the cooling time-scale becomes much longer than the others. As a
result, the shell holds the thermal energy for a longer time (see
Fig. A2b), and later it is converted into high momentum. With these
results, we chose 1 M resolution, which is fine enough to reproduce
the reasonably converged evolution of the SN shells.
APPENDIX B: METRICS FOR IMAGE QUALITY
This study uses two metrics, MAPE and MSSIM, to evaluate
our deep learning model. MAPE measures average reproducibility
across the entire image, while MSSIM measures local correlations
between images. Below, x = {xi| i ∈ N} and y = {yi| i ∈ N} denote
the densities of the ground truth (simulation result) and predicted
result, respectively.
B1 MAPE
MAPE is defined as
MAPE(x, y) =
1
N
N
i=1
yi − xi
xi
, (B1)
where N is the total number of voxels.
B2 MSSIM
SSIM is a metric for quality assessment based on the degradation
of structural information (Wang et al. 2004). It is commonly used
for the evaluation of image compression and restoration. SSIM is
defined as
SSIM(x, y) =
(2μxμy + C1)(2σxy + C2)
(μ2
x + μ2
y + C1)(σ2
x + σ2
y + C2)
. (B2)
where μx and μy (σx and σy) are the mean (variance) of x and y,
respectively, and σxy is the covariance of x and y. C1 and C2 are small
constants to avoid instability when the denominator is near zero. The
higher value of SSIM means that the two images are more similar.
The voxel-by-voxel match of the two images increases the value of
σxy and SSIM rather than the match on average.
In this study, we adopt C1 = 1.3 × 10−7
and C2 = 1.2 × 10−6
. In
general, SSIM is calculated at each local window with a given size
(e.g. Zeng Wang 2012; Dutta et al. 2019) and the average of them
is called Mean SSIM (MSSIM). The higher value of MSSIM also
means that the two images are more similar. We calculate a local
SSIM on each 8 × 8 × 8 block window. We divide a 3D volume
image with the size of 32 × 32 × 32 into 256(= 43
) blocks with the
size of 8 × 8 × 8 and take the MSSIM, i.e. the average SSIMs of the
divided blocks.
APPENDIX C: EXAMPLE RESULTS OF THE
PREDICTION
In Fig. C1, we present four examples of the prediction with the
3D-MIM in order to show that our prediction does not strongly
depend on the initial gas distribution. In particular, we show the
predictions of the initial distribution with high density where we
need to integrate particles with significantly short time-steps. The
left, middle, and right columns show the initial distribution, the result
of SPH simulations, and the prediction by the model, respectively.
Panel I, II, III, and IV represent the predictions of the shell expansion
with the initial mean density in the region within 5 pc around the
explosion centre, which are 3.2 × 10, 2.1 × 102
, 3.7 × 102
, and
6.3 × 102
cm−3
, respectively. Panel I, which has a relatively low
density at the centre, shows a relatively spherical shell. In panel
II, a SN explodes surrounded by dense filaments, which prevent
the blastwave from propagating. In panels III and IV, a SN occurs
within a dense filament. The blastwave breaks the filament and
propagates farther in the sparse region. We confirmed that our model
can predict the inhomogeneous expansion of the shell in various
densities.
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Figure C1. The 3D-MIM’s prediction of the shell expansion in four different initial distributions. Panel I, II, III, and IV represent the prediction of those with
the initial mean density in the region within 5 pc around the explosion centre, which are 3.2 × 10, 2.1 × 102, 3.7 × 102, and 6.3 × 102 cm−3, respectively. The
symbols and lines represent the same as Fig. 3.
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