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-resolutio

n 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 1978Dark matter haloes form through gravitational

collapseGalaxies 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 1974Merger treeDensity 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( | )L M dL( | )P N M

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

Minfall - halo mass at infall time tinfall

‘Orphan’ galaxies – satellites without subhalos

vs. HOD: halo mass of today

Two steps

• Minfall →Mstars

• tform, tinfall →SFH

→Dn4000

The Millennium Simulation Springel et al. 2005

8

3 8 1

1

Cosmological parameters:

0.25, 0.045, 0.75

0.73, 1, 0.9

Particles: 2160 , 8.6 10

Boxsize: 500

m b

h n

N h M

h Mpc

Mstars vs. Minfall in semi-analytic catalogue Croton et al. 2006

Statistics reproduced vs. semi-analytic results

Stellar mass Function Correlation

Central, satellite & ‘orphan’

L & Minfall Luminosity Function

‘orphan’ galaxies

• Critical for correlation at small scales

• Fit stellar mass function

& clustering for different stellar mass bins

Application to SDSS

Separate relations for central/satellite give better fit

Fitted relations

• Mandelbaum et al. 2006

• Satellites are less massive than centrals

SDSS observation

central young & satellite old?

SAM including AGN feedback e.g. Croton et al. 2006; Bower et al. 2006

tform tinfall tpresent

Modelling SFH

Log(

SF

R)

central satellite

• Exponentially evolved SFR with time scales and( )c M ( )s M

Bruzual & Charlot 2003 model

• Concentrate on Dn4000 because of its weak dependence on dust

• Minfall Mstars metallicity

Gallazzi et al. 2005

• tform, tinfall, SFH

metallicity SFH BC03

Clustering dependence on SEDs

Dn4000 +Mstars

positions

,c s

Non-parametric fit

1/c c • For central galaxies, is parameterized by a sum of Gaussians:

( )s M

• For satellite galaxies, assume simple Gaussian dispersion for

Best-fit:

Constant SFR:

1/ 0c c

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• Dn4000 – local density relation

• VVDS & DEEP2 Cucciati et al. 2006 Cooper et al. 2006

redshifts: 0 0.3 0.8 1.5 2 3

Conclusions

A new statistical model of galaxy clustering• Double power-law form for Mstars ~ Minfall relation• Applied to SDSS: For a given Minfall, satellites are

less luminous and less massive than centrals

Clustering dependence on SEDs reproduced Massive central galaxies have ceased forming st

ars; At low stellar masses, a significant fraction of central galaxies have recent starbursts

Satellite galaxies of all masses have declining SFR, with ~ 2.5s Gyr

Thank You ！

Full non-parametric test

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