Subaru UM 2009/01/15 1 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

Subaru UM 2009/01/15 2 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

Subaru UM 2009/01/15 3 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 M High temperature intra-cluster gas 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 …

Subaru UM 2009/01/15 4 Observation: Deep Hα 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 z= D=95Mpc : Nearby rich, massive cluster Observation Subaru Telescope + SuprimeCam 34×27FOV Filters B Rc Hα We found a number of peculiar inter-galactic features in these data

Subaru UM 2009/01/15 5 Extended Ionized Gas around the Coma galaxies

Subaru UM 2009/01/15 6 D100 RB199 Extended Ionized Gas around the Coma galaxies

Subaru UM 2009/01/15 7 What are they

Subaru UM 2009/01/15 8 Two examples 1. The 60 kpc Optical Filament Associated with a Poststarburst Galaxy D Strange Filamentary Structures (``Fireballs'') around a Merger Galaxy RB199

Subaru UM 2009/01/ The Remarkable 60×2 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.

Subaru UM 2009/01/ kpc D100

Subaru UM 2009/01/15 11 H-alpha Surface Brightness 2× erg/s/cm 2 /arcsec 2 Size: 2×60kpc Mass: 10 8 M if fv Hα

Subaru UM 2009/01/15 12 Stripped gas Ram pressure Infalling galaxy Hot ICM : ρ ICM Infall velocity V gal Ram pressure stripping gas star Numerical Simulation by Roadiger 2008

Subaru UM 2009/01/15 13 Stripping radius by ram pressure stripping R strip 0.7 kpc Almost all the disk gas of D100 can be stripped by ram pressure stripping. * assuming an exponential disk

Subaru UM 2009/01/15 14 Velocity field Ram pressure stripping !! How to collimate ? ?? Velocity field of the H-alpha filament of D100

Subaru UM 2009/01/ 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 star background galaxies Member galaxy ? background galaxy

Subaru UM 2009/01/15 18 Bright knots r e 200 – 300 pc M R -13 mag mass 10 7 M (M/L=1) L Hα erg/s Hα blue knot blue filament

The filaments of the fireballs grow bluer with distance from the host galaxy RB199.

Subaru UM 2009/01/15 20 FUV on B NUV on B The fireballs are detected in FUV 1650A and NUV 2500A. (GALEX archive data) Star-formation rate at bright knots M /yr

Subaru UM 2009/01/15 21 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 Hα filaments Stripped gas Excitation mechanism ?

Subaru UM 2009/01/15 22 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

Subaru UM 2009/01/15 23 Stripping radius by ram pressure stripping R strip 1.2 kpc Almost all the disk gas of RB199 can be stripped by ram pressure stripping.

Subaru UM 2009/01/15 24 Numerical simulations by Kronberger et al (A&A, 481, 337) Similar structure (including star-formation) is reproduced by numerical simulation

Subaru UM 2009/01/15 25 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

Subaru UM 2009/01/15 26 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