Extended ionized gas regions around the Coma cluster galaxies

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Extended ionized gas regions around the Coma
cluster galaxies

• Michitoshi YOSHIDA
• Okayama Astrophysical Observatory, NAOJ
• with Masafumi Yagi, Sadanori Okamura, Yutaka
  Komiyama, Hisanori Furusawa, Nobunari Kashikawa,
  Yusei Koyama, Hitomi Yamanoi, Takashi Hattori

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ABSTRACT

• We discovered peculiar, large extended ionized
  gas regions around several galaxies in the Coma
  cluster.
• They have a common structural feature one-sided
  flows from the galaxy disks
• Detailed data-analysis was done for two of these
  objects ? I show them later
• Possible formation mechanism
• Ram pressure stripping by collision between
  galaxies infalling to the cluster with hot ICM ?
  plausible
• Tidal stripping by galaxy-galaxy interaction /
  galaxy-cluster interaction cannot be totally
  excluded.
• Excitation mechanism of the ionized gas
• still unknown shock ? thermal conduction ? or
  else ?
• We witness a phase of rapid gas removal from
  galaxies near the central region of a rich cluster

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Introduction Environmental Effects on Galaxy
Evolution

• Environment of galaxies affects galaxy evolution
  much.
• Clusters of galaxies ? Ideal laboratories for
  investigating environmental effects on galaxy
  evolution
• High number density of galaxies
• Strong gravitational field (1014-15 M?)
• High temperature intra-cluster gas (107-8 K)
• Observational evidence on galaxy evolution in
  clusters
• Morphological segregation (Morphology-Density
  relation), Butcher-Oemler effect, Rapid rise of
  faint-end LF, etc.
• Various models have been proposed for
  environmental effects on cluster galaxy evolution
  ? Which is the dominant mechanism ? ? still
  unknown.

In order to study this subject
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Observation Deep Ha Imaging of the Coma Cluster
of Galaxies

• Primary Aim
• Study star-formation activity and faint-end
  luminosity function in the core of rich cluster
  of galaxies
• ? environmental effect on evolution of
  cluster galaxies
• A part of an international multi-wavelength study
  of the Coma cluster
• Object
• Coma cluster (z0.0232?D95Mpc) Nearby rich,
  massive cluster
• Observation 2006 - 2007
• Subaru Telescope SuprimeCam 3427FOV
• FiltersB?Rc?Ha

We found a number of peculiar inter-galactic
features in these data
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Extended Ionized Gas around the Coma galaxies
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Extended Ionized Gas around the Coma galaxies
D100
RB199
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What are they?
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Two examples

1. The 60 kpc Optical Filament Associated with a
   Poststarburst Galaxy D100
2. Strange Filamentary Structures (Fireballs'')
   around a Merger Galaxy RB199

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1. The Remarkable 602 kpc Optical Filament
Associated with a Poststarburst Galaxy in the
Coma Cluster(Yagi, M. et al. 2007, ApJ, 660,
1209)

• Unusual long, narrow, straight H-alpha filament
  extending from a post-starburst galaxy D100 in
  the Coma cluster
• The filament has a length of 60 kpc and a width
  of 2 kpc.
• Formation mechanism
• Ram pressure stripping ?
• Gas stripped off from a merged dwarf galaxy ?
• Excitation mechanism of the filament is unknown.

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60kpc
D100
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Ha
H-alpha Surface Brightness 210-17
erg/s/cm2/arcsec2 Size 260kpc Mass 108
M? (if fv1)
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Ram pressure stripping
Infalling galaxy
Stripped gas
?star
Hot ICM ?ICM
?gas
Infall velocity Vgal
Ram pressure
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Stripping radius by ram pressure stripping
assuming an exponential disk

• Rstrip 0.7 kpc

Almost all the disk gas of D100 can be stripped
by ram pressure stripping.
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Velocity field
Velocity field of the H-alpha filament of D100
Ram pressure stripping !! How to collimate ? ? ??
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2. Strange Filamentary Structures (Fireballs'')
around a Merger Galaxy in the Coma Cluster of
Galaxies (Yoshida, M. et al. 2008, ApJ, 688,
918.)

• An unusual complex of narrow blue filaments,
  bright blue knots, and H-alpha emitting
  filaments, extending up to 80 kpc south from an
  EA galaxy RB199 in the Coma cluster.
• We call it fireballs.
• Strong Ha and UV emission appear in the bright
  knots.
• ?Star formation recently ceased in the blue
  filaments and now continues in the bright knots.
• The gas stripped by some mechanism from the disk
  of RB199 may be traveling in the inter- galactic
  space, forming stars left along its trajectory.

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background galaxies
star
Member galaxy ?
background galaxy
Fireballs
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2
4
3
1
5
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Bright knots re 200 300 pc MR -13 mag ?
mass 107 M? (M/L1)
LHa 1038 erg/s
blue knot
Ha
blue filament
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The filaments of the fireballs grow bluer with
distance from the host galaxy RB199.
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The fireballs are detected in FUV(1650A)
and NUV(2500A). (GALEX archive data)
FUV on B
Star-formation rate at bright knots ? 10-210-3
M?/yr
NUV on B
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Star formation

• The gas stripped by some mechanism from the disk
  of RB199 may be traveling in the inter- galactic
  space, forming stars left along its trajectory.
• knots ? SF sites blue filaments ? Trajectory of
  SF stream
• Ha filaments ? Stripped gas Excitation
  mechanism ?

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Formation mechanism of the fireballs

• Tidal stripping by galaxy-galaxy interaction
• Difficult to explain its peculiar morphology
• One-sided, multiple, straight filaments
• No stellar tidal tail
• The blue filaments consist of newly formed stars
• Tidal stripping by cluster gravitational
  potential
• tidal force ltlt disk gravity
• Ram pressure stripping by collision with ICM

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Stripping radius by ram pressure stripping

• Rstrip 1.2 kpc

Almost all the disk gas of RB199 can be stripped
by ram pressure stripping.
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Similar structure (including star-formation) is
reproduced by numerical simulation
Numerical simulations by Kronberger et al. 2008
(AA, 481, 337)
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Summary for two objects

• D100 Strange long straight filament
• RB199 Splash-like filaments star-formation in
  the inter-galactic space
• ?
• Ram pressure stripping is the most plausible
  formation-mechanism for both objects
• These objects are in rapid gas removal phase

Other objects? ? also in violent gas removal
phase
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Summary

• We discovered peculiar, large extended ionized
  gas regions around several galaxies in the Coma
  cluster.
• They have a common structural feature one-sided
  flows from the galaxy disks
• Detailed data-analysis was done for two of these
  objects ? shown in this talk
• Possible formation mechanism
• Ram pressure stripping ? plausible
• Tidal stripping by galaxy-galaxy interaction /
  galaxy-cluster interaction
• Excitation mechanism of the ionized gas
• still unknown shock ? thermal conduction ? or
  else ?
• We witness a phase of rapid gas removal from
  galaxies near the central region of a rich cluster