comparing with redshift surveys of galaxies. redshift surveys –brief review cfa -----2000 galaxies...
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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