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Extended ionized gas regions around the Coma cluster galaxies

Michitoshi YOSHIDAOkayama Astrophysical Observatory, NAOJ

with Masafumi Yagi, Sadanori Okamura, Yutaka Komiyama, Hisanori Furusawa, Nobunari Kashikawa, Yusei Koyama, Hit

omi Yamanoi, Takashi Hattori

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ABSTRACT We discovered peculiar, large extended ionized gas re

gions around several galaxies in the Coma cluster. They have a common structural feature; one-sided flo

ws from the galaxy disks Detailed data-analysis was done for two of these obje

cts 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 investigati

ng 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), B

utcher-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 Hα Imaging of the Coma Cluster of Galaxies

Primary Aim: Study star-formation activity and faint-end luminosity functio

n 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 　（ z=0.0232 、 D=95Mpc ） : Nearby rich, massive cluster

Observation ： 2006 - 2007 Subaru Telescope + SuprimeCam 34’×27’FOV Filters ： B 、 Rc 、 Hα

We found a number of peculiarinter-galactic features in these data

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Extended IonizedGas around theComa galaxies

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D100

RB199

Extended IonizedGas around theComa galaxies

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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 60×2 kpc Optical Filament Associated with a Poststarburst Galaxy i

n 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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H-alpha Surface Brightness～ 2×10-17 erg/s/cm2/arcsec2

Size: 　 2×60kpc

Mass: 　～ 108 M

（ if fv ～１）

Hα

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Stripped gas

Rampressure

Infalling galaxy

Hot ICM : ρICM

Infall velocity Vgal

Ram pressure stripping

∑gas

stargas

2galIGM

2

G

V

∑star

Numerical Simulation by Roadiger 2008

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Stripping radius by ram pressure stripping

4

0ICM2

gasstar0strip

strip

2ln5.0

: radius stripping

Rv

MMGRR

R

1

34ICM

0

Θ8

gas

Θ9

star

skm1500

cm103

kpc0.1

M10

M100.4

v

R

M

M

Rstrip ～　 0.7 kpc

Almost all the disk gas of D100 can bestripped by ram pressure stripping.

* assuming an exponential disk

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Velocity field

0 20 40 60 80 100 120 140

0

50

100

150

200

250

300

350

Vel

oci

ty (

km/s

)

Distance (arcsec)

Ram pressure stripping !!How to collimate ? ??

Velocity field of the H-alpha filament of D100

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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 E+A galaxy RB199 in the Coma cluster.

We call it “fireballs”. Strong Hα 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.

Fireballs

starbackground galaxies

Member galaxy ?

background galaxy

1

2

34

5

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Bright knots

re ～ 200 – 300 pcMR ～ -13 mag mass ～ 107 M (M/L=1)

LHα ～ 1038 erg/s

Hαblueknot

blue filament

The filaments of the “fireballs”grow bluer with distance fromthe host galaxy RB199.

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FUV on B

NUV on B

The “fireballs” aredetected inFUV （ 1650A ） andNUV （ 2500A ） .(GALEX archive data)

Star-formation rateat bright knots 10-2 ～ 10-3 M/yr

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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 streamHα 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 << disk gravity

Ram pressure stripping by collision with ICM

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Stripping radius by ram pressure stripping

4

0ICM2

gasstar0strip

strip

2ln5.0

: radius stripping

Rv

MMGRR

R

1

34ICM

0

Θ8

gas

Θ9

star

skm2000

cm10

kpc5.1

M10

M102.4

v

R

M

M

Rstrip ～　 1.2 kpc

Almost all the disk gas of RB199 can bestripped by ram pressure stripping.

Subaru UM 2009/01/15 24Numerical simulations by Kronberger et al. 2008 (A&A, 481, 337)

Similar structure (including star-formation) is reproduced by numerical simulation

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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