Xiaohu Yang (杨小虎 )

Shanghai Astronomical Observatory

Partner group of MPA

Collaborators: H.J. Mo (UMass), F.C. van den Bosch (MPIA), A. Pasquali (MPiA), S. Weinmann (MPA), etc.

Connecting Galaxies with dark matter halos

Galaxies are formed in dark matter halos How many galaxies are formed per halo? What luminosity does each galaxy have? Color? What is their spatial distribution?

GalaxiesDark matter

Outline

What is HOD/CLF?

Can we directly measure the HOD/CLF?

Can we model the evolution of the satellite galaxies? To probe the fate of the disrupted satellite galaxies

Galaxy

Matter

Galaxies are biased tracers of the dark matter

Jing et al. 1998

Galaxy bias

An novel scheme: HOD

Jing et al. 1998

Original HOD model:

One step further:

HOD for galaxies of different luminosities: P(N|M)

Conditional Luminosity Function: P(L|M)

Yang et al. 2003; van den Bosch et al.2003

(1) Better match/model observation / Put constraints on the galaxy formation

(2a) Better constrain the cosmology

van den Bosch et al. 2003b

(2b) Better constrain the cosmology

Progresses in HOD/CLF models

Probe the connection between galaxies and HOST halos The halo Occupations

e.g. Jing, Mo & Borner 1998; Berlind & Weinberg 2002; Zheng et al. 2005; 2008… The Conditional Luminosity Function

e.g. Yang et al. 2003; van den Bosch et al. 2003; 2007; Cooray 2006… The non-parametric CLF

e.g. Vale & Ostriker 2004; 2006; Conroy et al. 2006… Model the central and satellite galaxies separately

Log-normal distribution model for the central galaxies Yang et al. 2003; 2008; Zheng et al. 2006; Cooray 2006; van den Bosch et al. 2007

Power law or (modified) Schetchter form CLF for satellite galaxies Berlind & Weinberg 2002; Yang et al. 2003; van den Bosch et al. 2003

GalaxiesDark matter

Part II: Direct measurement?

The HOD/CLF model Need to assume a functional form Constrained using the observational data

Do we have direct measure of these functions? Yes! If the galaxies can be grouped according to their common halos…

Galaxy groups in the SDSS DR4 (Yang et al. 2007)Sky coverage: 4514 deg^2

Galaxies with redshifts: 369447 (408119)

Groups selected: 301237 (300049)

Galaxies are grouped according to their common halos Halo mass is assigned for each group The most massive galaxy is defined as the central galaxy

central and satellite galaxies, separately

Direct measurement: CLF & CSM

Yang et al. 2008a

central galaxy, as a function of host halo mass

Model the local central-halo relation

Part III: Model the satellite evolution Satellite galaxies are connected with subhalos

Before their accretion into host halos, they are central galaxies They may have different evolution process after their accretion into the

host halos Probe the evolution of the satellite galaxies

The original stellar mass? The survived stellar mass?

What we have? Observation: CSMF for satellite galaxies (survived) Observation: the central – host halo relation Theory: the models of the subhalo population (SHMF)

Assumption : If the subhalo at the time of its accretion into host halo and the host halo

have the same central – host halo relation, we can predict the original CSMF for satellite galaxies

Used in recent models: Vale & Ostriker 2006; Conroy et al. 2006; 2007;

2008; Cooray 2005

The subhalo mass functions

Giocoli et al. 2008

Predict the original satellite galaxy population

What we have? Observation: CSMF for satellite galaxies (survived) Observation: the central – host halo relation Theory: the models of the subhalo population (SHMF)

Assumption : If the subhalo and the host halo have the same central – host

halo relation, we can predict the original CSMF for satellite galaxies

Predictions…

(A1) The satellite: prediction (original) vs. observation (survived)

(A2) The satellite: part of them are either stripped or disrupted.

(B) various stellar mass in satellite galaxies

The fate of the disrupted satellite galaxies:

Case 1: merged to the central galaxies Case 2: remain scattered as intra-cluster (group) stars Case 3: in-between

Case 1 ruled out

Star formation in small

halos

Star formation quench

limit

The fraction of stellar mass associated with central galaxy

ICS observational proof

Our prediction of about 8

Gonzalez et al. 2005; 2007; ~ 90% light associated with central galaxies is in the ICS

A factor of 10 more light in ICS than in the central galaxy

Various observational proofs of ICS.

Main results

Observational constraints: The satellite galaxies in more massive subhalos are disrupted at a

higher fraction Star formation in the central galaxy is necessary to halos of mass

>10^{12.4}M_{sun} Not all the stars in the disrupted satellite galaxies are merged to

the central galaxy, especially in clusters. The large amount ICS observed by Gonzalez et al. is predicted in

our model . Impacts:

The galaxy formation models The amount of AGN feedback

Yang et al. 2008 b