Comparing with redshift surveys of 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.

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Comparing with redshift surveys of galaxies

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Comparing with redshift surveys of galaxies

Comparing with redshift surveys of galaxies


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?)


The role of different observations

The role of different observations


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


Comparing with redshift surveys of galaxies

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:


Comparing with redshift surveys of galaxies

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


Comparing with redshift surveys of galaxies

背 景 介 绍

测量方法


Comparing with redshift surveys of galaxies

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


Dependence of cf on physical properties li et al 2005a b

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


Comparing with redshift surveys of galaxies

  • 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)

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


Comparing with redshift surveys of galaxies

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

Bimodal distribution in the color-magnitude diagram (SDSS)


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


Comparing with redshift surveys of galaxies

Galaxies: red for E; blue for spirals

Dark matter


Comparing with redshift surveys of galaxies

理 论 比 较

构建SDSS的模拟样本

SDSS DR4 

L500 L100+L300


Agreement after the reduction of faint satellites

Agreement after the reduction of faint satellites


Comparing with redshift surveys of galaxies

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


Summary

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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