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Comparing with redshift surveys of galaxies

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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Comparing with redshift surveys of galaxies

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  1. Comparing with redshift surveys of galaxies

  2. Redshift surveys –brief review • CFA -----2000 galaxies (1983) • Las Campanas ----25000 galaxies (1996) • 2dF----250,000 galaxies (2003) • SDSS----900,000 galaxies (2008?)

  3. The role of different observations

  4. 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

  5. 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

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

  7. 背 景 介 绍 统计量 • 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：

  8. 背 景 介 绍 测量方法 • 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

  9. 背 景 介 绍 测量方法

  10. Redshift two-point correlation functions for DR2 (Li, C. et al. astroph/0509874; 0509873; see also Zehavi et al. 2005) 红移空间的星系两点相关函数

  11. 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

  12. 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。

  13. 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

  14. 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

  15. Bimodal distribution in the color-magnitude diagram (SDSS)

  16. 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)

  17. 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

  18. Galaxies: red for E; blue for spirals Dark matter

  19. 理 论 比 较 构建SDSS的模拟样本 SDSS DR4  L500 L100+L300

  20. Agreement after the reduction of faint satellites

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

  22. 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

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