Comparing with redshift surveys of galaxies

Redshift surveys –brief review

• CFA -----2000 galaxies (1983)

• Las Campanas ----25000 galaxies (1996)

• 2dF----250,000 galaxies (2003)

• SDSS----900,000 galaxies (2008?)

The role of different observations

Clustering and environment analysis

• The key is to account for the incompleteness correctly

• For example, two-point correlation function is measured very simply with DD(r)/RR(r)-1, where DD and RR are the number of pairs of galaxies in the observed sample and in the random sample respectively;

• The key is to construct the random sample correctly

Incompleteness or selection effects

• Magnitude limited sample----radial selection effect;

• Limiting magnitude variation (0.1 typically) across the survey region;

• Survey boundary;• Redshift measurement completeness;

– Sampling rate;– Magnitude dependent redshift incompleteness– Fiber collision

Random sample

• A sample of the points randomly distributed spatially but with the same observational selection effects

• 光度函数：– 单位体积、单位光度间隔内的星系平均数目

– Schechter function:

• 两点相关函数：– 与均匀随机场相比，在距离某个星系 r处发现另一个星系的额外几率

• 相对速度弥散：

**** exp)(

L

Ld

L

L

L

LdLL

背 景 介 绍 统计量

212

12 )](1[ dVdVrndP

212

21212 )( vvr

• 红移空间畸变：本征运动使星系看起来偏离膨胀背景• 红移空间 2PCF：沿视向，大尺度压扁，小尺度拉伸

背 景 介 绍 测量方法

背 景 介 绍 测量方法

Redshift two-point correlation functions for DR2 (Li, C. et al. astroph/0509874; 0509873; see also Zeh

avi et al. 2005)

红移空间的星系两点

相关函数

Dependence of CF on physical properties (Li et al. 2005a,b)

星系的成团性随颜色、光谱特

征（恒星形成的历史）和密集

参量、恒星质量面密度（星系

结构和形态）的变化

• Luminosity dependence of the bias (r_p=2.7 Mpc/h; Zehavi et al. 2005)

• Stellar mass dependence (Li, et al 2005a,b)

• 星系成团的幅度，即偏袒因子 b，随光度（上图）和恒星质量（下图）的变化。

Velocity dispersion vs. physical properties (Li, C. et al. 2005b)

星系的速度弥散随颜色、光

谱特征（恒星形成的历史）

和密集参量、恒星质量面密

度（星系结构和形态）的变

化

Velocity vs luminosity (Li, et al. 2005a,b)

星系相对运动的速

度弥散随光度的变

化，反映不同光度

的星系的暗物质结

构环境

Bimodal distribution in the color-magnitude diagram (SDSS)

Three ways of interpreting

• Halo Occupation Distribution (HOD) model (e.g. Jing et al. 1998; Yang et al 2003)

• Using galaxy formation models – Hydro/N-body simulations with star formation

(physical processes; id of galaxies? e.g. V. Springel et al. 2005)

– Semi-analytical models of galaxy formation + N-body simulations (e.g. Kauffmann et al. 1999)

Physical processes of galaxy formation

• Formation of dark halos; gas shock heated;• Gas cooled radiatively;• Stars formed from cold gas;• Massive stars short lived; form neutron stars and

supernova explosions• Explosions inject energy and metals into interstel

lar medium (hot+cold); heating and enrich---feedback effects

• Mergers of galaxies after their host halos merge;• Black hole formation and its AGN feedback

Dark matter

Galaxies: red for E; blue for spirals

理 论 比 较 构建 SDSS的模拟样本

SDSS DR4

L500 L100+L300

Agreement after the reduction of faint satellites

Subhalo resolved: the bimodal color-mag distribution is much better reproduced

Summary

• Main features of galaxies can be explained in current galaxy formation models;

• High precision modeling for galaxy formation is still challenging, for very complicated physical process