Modeling the dependence of galaxy clustering on stellar mass and SEDs Lan Wang Collaborators: Guinevere Kauffmann (MPA) Cheng Li (MPA/SHAO, USTC) Gabriella De Lucia (MPA)

Outline

• Introduction ： theory of galaxy formation • New parameterized models:  Modeling galaxy clustering in a high resolution simulation of structure formation  Modeling the dependence of clustering on spectra energy distributions of galaxies

Galaxy formation

• Galaxy formation includes two steps: e.g.

White & Rees 1978

 Dark matter haloes form through gravitational collapse  Galaxies form in dark matter halos by cooling of baryonic material — physical processes ： gas cooling, star formation, SN feedback, AGN feedback, mergers etc.

Properties of dark matter haloes

Cold dark matter cosmology: structures grow hierarchically • Dark matter halos ：  Abundance

Press & Schechter 1974

 Merger tree  Density profile (NFW)

Navarro, Frenk & White 1996,1997

Link galaxy properties to DM halos • Hydrodynamic Simulation e.g.

White, Hernquist & Springel 2001

• Semi-analytic models

Kauffmann et al. 1999

• Halo Occupation Distribution models (HOD) | )

Berlind & Weinberg 2002

 )

Yang, Mo & van den Bosch 2003

SAM HOD

Our Methodology

• •   Falls in between semi-analytic method & HOD approach: Positions, velocities and formation history from simulation Parameterized functions to determine galaxy properties Based on

Millennium Simulation

M infall - halo mass at infall time t infall ‘Orphan’ galaxies – satellites without subhalos vs. HOD: halo mass of today Two steps • M infall →M stars • t form , t infall →SFH →D n 4000

The Millennium Simulation

Springel et al. 2005

Cosmological parameters:  

m h

 0.25,  

b

0.73,

n

 1,  8 0.045,    0.9

0.75

Particles:

N

 3  8  1

h M

 1 Boxsize: 500

h Mpc

M stars vs. M infall in semi-analytic catalogue

Croton et al. 2006

Statistics reproduced

vs.

semi-analytic results Stellar mass Function Correlation

Central, satellite & ‘orphan’ L & M infall Luminosity Function

‘orphan’ galaxies

• Critical for correlation at small scales

Application to SDSS

• Fit stellar mass function & clustering for different stellar mass bins Separate relations for central/satellite give better fit

Fitted relations

• Satellites are less massive than centrals •

Mandelbaum et al. 2006

SDSS observation

central young & satellite old?

 SAM including AGN feedback e.g.

Croton et al. 2006; Bower et al. 2006

Modelling SFH

• Exponentially evolved SFR with time scales 

c

(

M

 ) and 

s

(

M

 ) central satellite t form t infall t present

Bruzual & Charlot 2003 model

• Concentrate on D n 4000 because of its weak dependence on dust

Clustering dependence on SEDs • M infall M stars metallicity

Gallazzi et al. 2005

• t form , t infall  

c s

 metallicity SFH

BC03

D n 4000 + M stars positions

Non-parametric fit



c

 

c

parameterized by a sum of Gaussians: • For satellite galaxies, assume simple Gaussian dispersion for 

s

(

M

 )

Best-fit:

Constant SFR: 

c

 1/ 

c

 0 0

Main results

• Massive centrals have ceased forming stars • At low stellar masses, central galaxies display a wide range of different SFH, with a significant fraction experiencing recent star bursts.

• Time scale for satellite galaxies is almost independent of stellar mass

Consistency checks

• Specific SFR: our model

vs.

SDSS results • g-r distributions

SFH: compared with SAM

(

De Lucia & Blaizot 2006

) • e-folding time scale for satellites our model: ~2-2.5 Gyr SAM: ~1Gyr

Evolution to higher redshifts

• D n 4000 – local density relation redshifts: 0 0.3

0.8

1.5

2 3 • VVDS & DEEP2

Cucciati et al. 2006 Cooper et al. 2006

Conclusions

A new statistical model of galaxy clustering • Double power-law form for M stars ~ M infall relation • Applied to SDSS: For a given M infall , satellites are less luminous and less massive than centrals  Clustering dependence on SEDs reproduced  Massive central galaxies have ceased forming stars; At low stellar masses, a significant fraction of central galaxies have recent starbursts  Satellite galaxies of all masses have declining SFR, with 

s

~ 2.5

Gyr

Thank You

！

Full non-parametric test

• Time scale for satellite galaxies is almost independent of stellar mass