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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


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


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:


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


背 景 介 绍

测量方法


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)

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

  • Mergers of galaxies after their host halos merge;

  • Black hole formation and its AGN feedback


Galaxies: red for E; blue for spirals

Dark matter


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


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