Formation of Galaxies in Clusters Myung Gyoon Lee Seoul National University Astronomy Program, SEES The 1st KIAS International Workshop on Cosmology and Structure Formation, Seoul (Abell 2255 from SDSS)

2 Prelude  Formation of Clusters & Large Scale Structures Can be described by only mass and gravity A simple model of hierarchical merging in CDM cosmology  Formation of Galaxies What is a galaxy? ->a system of mass+gas+stars embedded in DM halos, showing diverse morphological kinds. We need to explain both mass assembly & star formation history. Not a simple problem A longstanding, but still intriguing & exciting problem

3 Today  Formation of Galaxies in Clusters Focusing on massive early-type galaxies in clusters 1. Overview of recent progress: two examples 2. Introducing our work 1) Globular Clusters in gEs of the Virgo cluster 2) Age and metallicity of Es in nearby clusters 3) Kinematics of galaxies in nearby clusters 4) Early-type galaxies in the GOODS/ACS field 3. Our plan with SDSS data 4. Summary

4 Galaxy Clusters  Galaxy clusters are the largest gravitationally bound system, composed of galaxies.  Catalogs: A few examples Abell (1958), Abell et al (1989): 4073 for all sky of PSS Bahcall et al (2003): 799 (53 Abell clusters+ new) from early SDSS data (more to come) Bohringer et al (2004): 447 from REFLEX cluster survey  Recent Refs  Rosati etal (2002) The Evol of X-ray Clusters of Galaxies, ARAA, 40, 539  Mulchay et al (2004) Clusters of Galaxies: Probes of Cosmoloigcal Struc and Gal Evol  Voit (2004) Tracing Cosmic Evolution of Clusters of Galaxies, Rev.Mod.Phys.

5 Why galaxies in clusters?  Member galaxies at the same distance  Easily identified in the sky  A cluster occupies a small region in the sky.  Abundant with early type galaxies ( LG)  We can study environmental effects on galaxies.  Clusters are ideal to investigate the formation & evolution of galaxies and clusters.

6 Recent Progress: Two examples  1) Nearby galaxies at 0.08< z<0.12  2) A sample of clusters at 0.3<z<1.0

7 CMR  Environments  Hogg et al (2004 ApJ,601,L29): 55,158 SDSS galaxies at 0.08<z<0.12 (see also Blanton et al 2003, ApJ, 594, 186)  (Results) Bulge-dominated(Sersic n>2) galaxies show much redder and much narrower than disk-dominated galaxies(n<2). More bulge galaxies in the higher density regions. CMR almost independent of density (d(g-r)<0.02)!! Corresponding to a change in age or metallicity <20%.  Random merger of low L galaxies->a large spread However, need to look at wider colors !

8 Cluster Galaxy Evolution up to z=1  Andreon et al (2004, MN, 353, 353) (Kodama et al 1998, Stanford et al 1998)  Colors and LF of 24 clusters at 0.3<z<1 (mostly X-ray clusters)  Consistent with the presence of two populations: 1) CMR of the brightest galaxies -> old systems formed at z f =2-5 2) m* in LF-> younger systems showing more recent SF at z f <1.

9 Our Studies (2004) Primary goal: Understanding the formation & evolution of galaxies from z=0 to high z. 1) Globular Clusters in gEs of the Virgo cluster 2) Formation of Galaxies in Nearby Abell Clusters 3) Kinematics of Galaxies in Nearby Abell Clusters 4) Early-type Galaxies in the GOODS/ACS Field Our team: Hong Soo Park, Ho Seong Hwang, Tae Hyun Kim, Joon Hyeop Lee and more

10 1. Virgo Cluster  D=15 Mpc, z=  The nearest cluster including the Local Group.  Irregular (dynamically young), low mass cluster.  Ideal to study in detail the stars and clusters in gEs.

11 Virgo Map

12 Virgo gEs M87M47M60 M86 M84 NGC 4636

13 Virgo gEs  Virgo gEs Name M V SNSN N GC Remark M cD M The brightest M M M N

14 GCs in M49 (gE)

15 CMD-wide field  Observations KPNO4m+PFCCD 16 ’ x16 ’ Geisler,Kims,Park,Lee Washington filters CT 1 (efficient for EGCs)  Three kinds GCs (BGC, RGC) galactic stars background galaxies (Lee et al 04) BGC RGC

16 Color distribution  Variety with d[color]=const  N(BGC)/N(RGC) varies depending on gEs (Lee et al 03)

17 GC-Host galaxies  Color, velocity dispersion, Mv, Mg2 (Lee 2003)  Strong correlations between RGC and stellar halo,  No for BGC  RGCs follow the stellar halo, but BGCs do not!!!!

18 Models for gE formaton  How gEs formed?  Two competing models: 1) Monolithic Collapse Models (MCM): old soldiers never die. (Eggen, Lynden-Bell, Sandage 1962: MW Halo) (Partridge & Peebles 1967, Tinsley 1972, Larson 1974, Chiosi & Carraro 2002) 2) Hierarchical Merging Models (HMM) : current paradigm (Toomre 1977, Searle & Zinn 1978, Kauffmann et al 1993, Steinmetz & Navarro 2002)

19 Formation of gEs from GCs  When & How long BGC, RGC, gE formed? BGCs formed at 12.5G RGCs+gE* formed at 10.5 G  How they formed? HMM+MCM With HMM making gE at z>2! (current models) With rapid chemical enrichment

20 2. CMR of Nearby Clusters

A photometric study on the formation of galaxies in nearby galaxy clusters Tae Hyun Kim, Myung Gyoon Lee Seoul National University KAS Meeting 2004 Fall

22 Observation & Data  BOAO (June 2~5, 2003), B,V,I  2MASS Extended Source Catalog, Ks  Objects KAS Meeting 2004 Fall

23 A1656 (Coma) Color Color-Magnitude Relation

24 Color-Magnitude Relation No significant evolutions in slope, scatter, zero points

25 Brighter galaxies have redder color. What makes galaxies red ? –Age & Metallicity ’Age-metallicity degeneracy’  ’Age-metallicity degeneracy’ How to break it? With NIR band color Which is less sensitive to age. Combining Optical & NIR color  Break ‘Age-metallicity-degeneracy’ Color Color-Magnitude Relation

26 SSP Models Bruzual & Charlot (2003) Vazdekis (1999) Kurth (1999) Worthey (1994) Age, [Fe/H]: relative Various combinations of Stellar library Evolutionary track IMF Age : major recent SFH CCD

27 BC2003 Worthey1994 Model Comparison KAS Meeting 2004 Fall

28

29 2 Gyrs >10 Gyrs

30 Summary  Early type galaxies in each cluster show a large spread in age and metallicity.  Luminosity weighted mean ages range in narrow region, 5~7Gyrs  Luminosity weighted mean [Fe/H] is 0.09~0.56. KAS Meeting 2004 Fall

Clusters with SDSS data Abell 168 Abell 2199 Abell 2255

32 Comparison with Phot & Spec Photometric Data with SSP model of Bruzual & Charlot 2003 Spectroscopic Data with SSP model of Bruzual & Charlot 2003

33 Abell 168, Abell 119

34 Abell 2199, Abell 2255

35 Averages of galaxies  Compared with BOAO results.

36 3. Kinematics of Abell 2255

37 Abell 2255 Massive (vel disp=1221 km/s) z= (d=300 Mpc) Two cDs (dv=2600km/s)-> merging? [Burns et al 1995] X-ray peak off from the optical peak [SDSS DR2]

38 Goals From the velocity data of galaxies in rich galaxy clusters, we will derive ; Basic kinematics : Rotation, Velocity dispersion Finding Substructure The orbits of different types of galaxies in galaxy clusters  Understanding the formation and dynamical evolution of galaxy and galaxy clusters.

39 Membership of Abell 2255 Asymmetric

40 D-S plot for A2255  D-S Delta (differences in v and v dispersion. Dressler & Schechtman 1988)-circle sizes  Found one small substructure!

41 X-ray vs Number density

42 Morphological class  Criteria: image+spectra (templates: Strateva et al 2001) 268=166 Early + 47 Int + 55 Late

43 SB Profiles & Concentration parameter

44 Spatial distribution  Early types show strong central concentration.  A small substructure show mostly early types.

45 V vs mag & color  Some difference of velocity spread depending on colors.

46 V vs radius & PA  Velocity dispersion decreases with R.  Rotation is not clearly seen.

47 Discussion  To be compared with numerical simulation

48 4. GOODS/ACS red: early (C>3 &A 0.3), green: intermediate, black: no class B<25 –Concentraton : (80% light radius)/(20% light radius) –Rotational asymmetry : ½ (∑ ((pixel value) – (180 o rotated pixel value)) / ∑ (pixel value))

49 Evolution of Early types - Simple Stellar Population (SSP; star forming as delta function) - Single Burst (constant star forming for early 1Gyr) - Exponentially Decreasing (exponentially decreasing SFR with scale time 1Gyr) - Linearly Decreasing (linearly decreasing SFR with SFR=0 at 10Gyr) - Constant Star-Formation (constant SFR = 1 M ⊙ /yr)

50 Red (c>3), z= Blue (c>3) Blue (c<3), z= Blue (c<3), z= Red (c<3)

51 Our plan with SDSS  Nearby clusters SDSS+2MASS Increasing N of nearby clusters To study the effects of type(e.g. regular and irregular), mass, environments  Higher-z clusters Increasing z To look at evolution of clusters Using larger telescopes

52 Summary  Current status of our understanding how massive galaxies in clusters formed?  Intriguing!  What do we need for better?  More data?  More galaxies? nearby ones or distant ones?  More models? (MCM and HMM are pretty old)  New ideas for analysis and models ?  Hope to get some during this workshop and be able to show some progress next time.