1. Haro
2
MRK
178
NGC
2366
UM
417
MRK
178
MRK
1416
UM
323
UM
417
NGC
2366
Tim
Costa1
&
Laura
Congreve
Hunter2
1.
University
of
Massachusetts
at
Amherst,
2.
Mount
Holyoke
College
Searching
for
Renegade
Ionizing
Radiation
in
Blue
Compact
Dwarf
Galaxies
Acknowledgments:
Five
College
Astronomy
Department,
Dr.
Anne
Jaskot,
Michael
Peterson,
Kitt
Peak
National
Observatory
References:
Bouwens,
R.
et
al,
2010,
ApJ,
708,
L69;
Izotov,
Y.
et
al,
2016,
Nature,
529,
178.;
Leitherer,
C.
et
al,
2016,
ArXiv
e-­‐prints,
arXiv:
1603.06779.;
Pellegrini
et
al.
2012,
ApJ
755,
40.;
Shull,
J
et
al.
2012,
ApJ,
747,
100.;
Zastrow,
J
et
al.
2013.
ApJ,
779,
76
Abstract
The
reionization
of
the
universe
took
place
between
z~11
and
z~6
and
astronomers
debate
the
method
for
reionization.
We
cannot
con`irm
galaxies
reionized
the
universe
because
we
know
of
only
a
handful
of
galaxies
with
escaping
ionizing
radiation
(Shull
et
al.
2012.)
By
looking
at
the
ratio
between
[OIII]
and
either
[SII]
or
[OII]
we
searched
for
highly
ionized
regions
with
possibly
escaping
ionizing
radiation.
We
use
low
redshift
Blue
Compact
Dwarfs
(BCDs)
as
proxies
for
star
forming
galaxies
from
the
early
Universe
because
of
their
high
star
formation
rates
(SFRs)
(Izotov
et
al.
2016.)
Three
of
our
seven
galaxies
have
areas
with
potential
to
be
classi`ied
as
optically
thin
and
might
be
regions
where
ionizing
radiation
could
escape.
Figure
1
An
[OIII]/[SII]
emission
line
ratio
map
of
the
Small
Magellanic
Cloud.
Darker
regions
indicate
higher
values.
(Pellegrini
et
al.
2012.)
Green
arrows:
Low
[O
III]/[S
II]
rim,
Optically
thick,
Purple
arrow:
High
[O
III]/[S
II]
throughout,
Optically
thin.
Motivation
∎
Almost
all
known
star-­‐forming
galaxies
have
little
to
no
escaping
ionizing
radiation
∎ The
Universe
was
reionized;
the
method
by
which
is
an
open
question
with
quasars
and
starburst
galaxies
as
the
most
likely
options
(Zastrow
et
al.
2013)
∎ Previous
detections
of
escaping
Lyman
Continuum
radiation
from
only
`ive
low
redshift
galaxies
(Izotov
et
al.
2016,
and
Leitherer
et
al.
2016)
∎ Highest
observed
escape
fraction
is
about
8%
∎ Reionization
requires
a
mean
escape
fraction
of
at
least
20%
(Bouwens
et
al.
2010)
Analysis
∎ Observed
seven
isolated,
low
redshift
BCDs
∎ Early
universe
is
hard
to
observe
so
we
instead
used
nearby
proxies
∎ BCDs
are
small
starburst
galaxies
and
may
be
similar
to
galaxies
that
existed
in
the
early
universe
∎ Observing
∎ Used
WIYN
.9
m
telescope
∎ Observed
in
[OIII],
[OII]
or
[SII],
R,
U,
and
V
∎ Reductions
∎ Basic
reduction
methods
such
as
bias
subtractions
and
`lat
`ield
corrections
∎ Isolated
emission
lines
by
subtracting
scaled
continuum
images
from
the
narrowband
images
∎ Converted
counts
to
`lux
Figure
2:
From
left
to
right:
MRK
1416
ionization
parameter
map,
MRK
1416
singly
ionized
gas
isophote,
and
MRK1416
limit
map.
Brighter
regions
indicate
a
higher
[OIII]/[SII]
ratio.
As
seen
in
the
ionization
parameter
map
and
isophote,
we
did
not
have
detections
greater
than
3
sigma
above
the
noise
for
MRK
1416.
Results
Cont.
Observations
Conclusions
Of
the
seven
galaxies
we
analyzed,
we
found
three
that
may
have
optically
thin
areas
and
might
be
candidates
for
galaxies
with
escaping
ionizing
radiation:
Haro
2,
NGC
2366,
and
MRK
178.
With
the
data
we
collected,
we
have
no
reason
to
believe
that
the
other
four
galaxies
have
areas
where
ionizing
radiation
is
likely
to
be
escaping.
With
that
being
said,
our
study
was
limited
by
the
resolution
of
our
telescope
and
the
inherent
weakness
of
the
detections
in
[OII]
and
[SII].
As
such,
optically
thin
areas
may
also
be
surrounded
by
singly
ionized
gas
that
we
failed
to
detect.
We
suggest
future
studies
of
these
galaxies
and
others
like
them,
using
higher
resolution
instruments.
By
their
very
nature,
BCDs
tend
to
be
small
galaxies
which
makes
resolving
structure
in
them
dif`icult
without
proper
resolution.
Our
results
neither
con`irm
or
refute
starburst
galaxies
as
possible
sources
for
reionization
so
further
study
of
these
galaxies
is
still
necessary.
Three
color
images
of
our
galaxies
showing
distribuPon
of
the
differently
ionized
gases.
Blue
is
the
singly
ionized
gas
([OII]
or[SII]),
the
green
is
the
[OIII]
and
the
red
is
the
V
filter
images
to
give
over
all
morphology
of
the
galaxies.
The
possible
opPcally
thin
areas
are
indicated
by
purple
arrows)
Galaxies
that
were
not
considered
to
have
optically
thin
area
either
had
no
projections
that
showed
dramatic
drops
in
ionization
ratio
or
were
no
resolved
enough
to
show
any
`ine
structure.
Results
∎ Ionization
Parameter
Maps
(See
Figure
1)
∎ Detecting
Lyman
Continuum
is
dif`icult
because
it
is
in
the
far
UV
and
the
escaping
streams
have
directional
bias
(can
only
be
directly
detected
if
escaping
photons
escape
toward
us)
∎ Divide
`lux
calibrated
images
of
doubly
ionized
gas
[OIII]
by
images
of
singly
ionized
gas
[OII]
or
[SII]
∎ Ratio
of
the
gases
may
show
areas
with
an
abundance
of
[OIII]
which
may
be
optically
thin
areas
∎ Optically
thin
areas
will
have
a
higher
[OIII]/[OII]
or
higher
[OIII]/[SII]
ratio
throughout
the
area,
while
optically
thick
areas
will
transition
to
lower
ratios
of
[OIII]/[OII]
or
[OIII/
SII]
(Zastrow
et
al.
2013.)
∎ Isophotes
can
show
trends
in
the
positions
of
ionized
gas
∎ Limit
Maps
(See
Figure
2)
∎ [SII]
is
inherently
weak
and
[OII]
is
far
into
the
blue
which
limits
their
detectability
∎ In
some
cases,
we
did
not
get
any
reliable
detections(
>3σ)
of
[OII]
and
[SII]
∎ Set
upper
limits
based
on
3σ
values
which
correspond
to
lower
limit
for
[OIII]/[OII]
and
[OIII]/[SII]
values
6
arc
seconds
From
top
to
bottom:
Haro
2
limit
map
with
projection,
MRK
178
ionization
parameter
map
with
projection,
NGC2366
ionization
parameter
map
with
projection,
and
UM
417
limit
map
with
projection.
18
arc
seconds
12
arc
seconds
12
arc
seconds
The
projections
show
the
transition
from
a
highly
ionized
area
to
one
that
is
background
level.
Notice
for
the
`irst
three,
the
transition
is
abrupt,
indicating
possibly
optically
thin
areas
(marked
in
the
images
by
purple
arrows).
For
UM
417
the
transition
between
high
ionization
to
background
is
more
gradual.
Haro
2
J
1044
MRK
178
MRK
1416
UM
323
UM
417
NGC
2366