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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.

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redshift surveys brief review
Redshift surveys –brief review
  • CFA -----2000 galaxies (1983)
  • Las Campanas ----25000 galaxies (1996)
  • 2dF----250,000 galaxies (2003)
  • SDSS----900,000 galaxies (2008?)
clustering and environment analysis
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
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
Random sample
  • A sample of the points randomly distributed spatially but with the same observational selection effects

背 景 介 绍


  • 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:

背 景 介 绍


  • 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


Redshift two-point correlation functions for DR2 (Li, C. et al. astroph/0509874; 0509873; see also Zehavi et al. 2005)


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


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



Velocity vs


(Li, et al.



three ways of interpreting
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
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 interstellar medium (hot+cold); heating and enrich---feedback effects
  • Mergers of galaxies after their host halos merge;
  • Black hole formation and its AGN feedback

理 论 比 较



L500 L100+L300

  • 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