Formation of Galaxies in Clusters

Myung Gyoon Lee

Seoul National UniversityAstronomy Program, SEES

2004. 10.28-29 The 1st KIAS International Workshop

on Cosmology and Structure Formation, Seoul

(Abell 2255 from SDSS)

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Prelude

Formation of Clusters & Large Scale Structures

Can be described by only mass and gravityA simple model of hierarchical merging in CDM cosmology

Formation of GalaxiesWhat 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 problemA longstanding, but still intriguing & exciting problem

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Today

Formation of Galaxies in ClustersFocusing on massive early-type galaxies in clusters

1. Overview of recent progress: two examples2. Introducing our work

1) Globular Clusters in gEs of the Virgo cluster2) Age and metallicity of Es in nearby clusters3) Kinematics of galaxies in nearby clusters4) Early-type galaxies in the GOODS/ACS field

3. Our plan with SDSS data4. Summary

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Galaxy Clusters

Galaxy clusters are the largest gravitationally bound system, composed of 102-103 galaxies.

Catalogs: A few examplesAbell (1958), Abell et al (1989): 4073 for all sky of PSSBahcall 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.

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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.

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Recent Progress: Two examples

1) Nearby galaxies at 0.08< z<0.12 2) A sample of clusters at 0.3<z<1.0

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CMREnvironments

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 !

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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 zf=2-5

2) m* in LF-> younger systems showing more recent SF at zf<1.

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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 cluster2) Formation of Galaxies in Nearby Abell Clusters3) Kinematics of Galaxies in Nearby Abell Clusters4) Early-type Galaxies in the GOODS/ACS Field

Our team: Hong Soo Park, Ho Seong Hwang, Tae Hyun Kim, Joon Hyeop Lee and more

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1. Virgo Cluster

D=15 Mpc, z=0.0039The nearest cluster including the Local Group.Irregular (dynamically young), low mass cluster .Ideal to study in detail the stars and clusters in gEs.

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Virgo Map

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Virgo gEs

M87 M47 M60

M86 M84 NGC 4636

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Virgo gEs

Virgo gEs

Name MV SN NGC Remark

M87 -22.4 14 13000 cD

M49 -22.6 6 6000 The brightest

M60 -22.2 7 5000

M86 -21.8 6 3000

M84 -21.7 7 3000

N4636 -21.7 8 4000

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GCs in M49 (gE)

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CMD-wide field

ObservationsKPNO4m+PFCCD16’x16’Geisler,Kims,Park,LeeWashington filters CT1

(efficient for EGCs)

Three kindsGCs (BGC, RGC)galactic starsbackground galaxies

(Lee et al 04)

BGC RGC

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Color distribution

Variety with d[color]=const N(BGC)/N(RGC) varies depending on gEs

(Lee et al 03)

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GC-Host galaxies

Color, velocity dispersion, Mv, Mg2

(Lee 2003) Strong correlations betwe

en RGC and stellar halo, No for BGC RGCs follow the stellar ha

lo, but BGCs do not!!!!

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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)

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Formation of gEs from GCs

When & How long BGC, RGC, gE formed?

BGCs formed at 12.5GRGCs+gE* formed at 10.5 G

How they formed?HMM+MCMWith HMM making gE at z>2! (current models)With rapid chemical enrichment

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2. CMR of Nearby Clusters

A photometric study on the formation of galaxies

in nearby galaxy clusters

Tae Hyun Kim , Myung Gyoon LeeSeoul National University

KAS Meeting2004 Fall

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Observation& Data

BOAO (June 2~5, 2003), B,V,I 2MASS Extended Source Catalog, Ks Objects

KAS Meeting2004 Fall

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A1656 (Coma)

CCoolloorr-Magnitude Relation

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Color-Magnitude Relation

•No significant evolutions in slope, scatter, zero points

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• Brighter galaxies have redder color.

• What makes galaxies red ?– Age & Metallicity

’’Age-metallicity degeneracy’Age-metallicity degeneracy’

• How to break it? With NIR band colorWhich is less sensitive to age.

• Combining Optical & NIR color Break ‘Age-metallicity-degeneracy’

CCoolloorr-Magnitude Relation

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SSP Models

Bruzual & Charlot(2003)

Vazdekis(1999)

Kurth(1999)

Worthey(1994)

Age, [Fe/H]: relativeVarious combinations of

• Stellar library• Evolutionary track• IMF

• Age : major recent SFH

CCD

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BC2003 Worthey1994

Model Comparison

KAS Meeting2004 Fall

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2 Gyrs

>10 Gyrs

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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 Meeting2004 Fall

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2.1 Clusters with SDSS data

Abell 168 Abell 2199Abell 168 Abell 2199

Abell 2255Abell 2255

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Comparison with Phot & Spec

Photometric Data with SSP model of Bruzual & Charlot 2003

Spectroscopic Data with SSP model of Bruzual & Charlot 2003

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Abell 168, Abell 119

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Abell 2199, Abell 2255

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Averages of galaxies

Compared with BOAO results.

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3. Kinematics of Abell 2255

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Abell 2255

Massive (vel disp=1221 km/s)

z=0.0808 (d=300 Mpc)

Two cDs (dv=2600km/s)-> merging? [Burns et al 1995]

X-ray peak off from the optical peak [SDSS DR2]

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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.

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Membership of Abell 2255

Asymmetric

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D-S plot for A2255

D-S Delta (differences in v and v dispersion. Dressler & Schechtman 1988)-circle sizes

Found one small substructure!

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X-ray vs Number density

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Morphological class

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

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SB Profiles & Concentration parameter

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Spatial distribution

Early types show strong central concentration.

A small substructure show mostly early types.

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V vs mag & color

Some difference of velocity spread depending on colors.

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V vs radius & PA

Velocity dispersion decreases with R.

Rotation is not clearly seen.

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Discussion

To be compared with numerical simulation

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4. GOODS/ACS

red: early (C>3 &A<0.3), blue:late-type (C<3 &A>0.3), green: intermediate, black:

no class

B<25

–Concentraton : (80% light radius)/(20% light radius)

–Rotational asymmetry : ½ (∑ ((pixel value) – (180o rotated pixel value)) / ∑ (pixel value))

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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)

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Red (c>3), Red (c>3), z=0.8-1.0z=0.8-1.0

Blue (c>3)Blue (c>3)

Blue (c<3), Blue (c<3), z=1.0-1.2z=1.0-1.2

Red (c<3)Red (c<3)

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Our plan with SDSS

Nearby clusters SDSS+2MASSIncreasing N of nearby clustersTo study the effects of type(e.g. regular and irregular), mass , environments

Higher-z clustersIncreasing zTo look at evolution of clustersUsing larger telescopes

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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.