Brighter galaxy bias: underestimating the velocity dispersions of galaxy clusters
Brighter galaxy bias: underestimating the velocity dispersions of galaxy clusters
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DOI：
10.1093/mnras/stt1201
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发表时间：
2013-06
影响因子：
4.8
通讯作者：
L. Old;Meghan E. Gray;F. Pearce
中科院分区：
文献类型：
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作者：
L. Old;Meghan E. Gray;F. Pearce
我们研究了在选择较亮星系团的光谱红移来估计模拟和观测星系目录中星系团的速度色散时引入的系统偏差。我们从公开的De Lucia & Blaziot半解析模型星系表中选取了Ngal > 50的星系团，在五个低红移的快照上。星团也选自坦普尔SDSS DR 8集团和集群目录的红移范围0.021 6 z 6 0.098。我们采用各种选择技术来探索速度色散偏差是否仅仅是由于缺乏动力学信息，或者是集群中发生的潜在物理过程的结果，例如，较亮的集群成员所经历的动力学摩擦。的父暗物质（DM）晕的速度分散体相比，星系团的分散体和DM粒子速度的堆叠分布旁边相应的星系速度分布进行检查。我们发现晕和半解析星系团的速度色散之间存在明显的偏差，其数量级为σgal/σDM-0.87 ~ 0.95，而堆积星系和DM粒子的速度分布则存在明显的差异。我们确定了一个系统的低估的速度色散时，施加增加绝对I波段的幅度限制。这种低估增强时，只使用较亮的集群成员的动力学分析的顺序为5 - 35%，表明动力学摩擦是一个严重的来源时，使用星系速度示踪剂的基础引力势的偏见。在文献中，我们发现，由此产生的偏见不仅是晕质量依赖，但依赖的性质根据星系选择策略的变化。我们提出一个建议，在现实的情况下，有限的光谱观测，一个严格的震级限制的样本应避免，以确保无偏估计的速度色散。
We study the systematic bias introduced when selecting the spectroscopic redshifts of brighter cluster galaxies to estimate the velocity dispersion of galaxy clusters from both simulated and observational galaxy catalogues. We select clusters with Ngal > 50 at five low redshift snapshots from the publicly available De Lucia & Blaziot semi-analytic model galaxy catalogue. Clusters are also selected from the Tempel SDSS DR8 groups and clusters catalogue across the redshift range 0.021 6 z 6 0.098. We employ various selection techniques to explore whether the velocity dispersion bias is simply due to a lack of dynamical information or is the result of an underlying physical process occurring in the cluster, for example, dynamical friction experienced by the brighter cluster members. The velocity dispersions of the parent dark matter (DM) halos are compared to the galaxy cluster dispersions and the stacked distribution of DM particle velocities are examined alongside the corresponding galaxy velocity distribution. We find a clear bias between the halo and the semi-analytic galaxy cluster velocity dispersion on the order of σgal/σDM � 0.87 0.95 and a distinct difference in the stacked galaxy and DM particle velocities distribution. We identify a systematic underestimation of the velocity dispersions when imposing increasing absolute I-band magnitude limits. This underestimation is enhanced when using only the brighter cluster members for dynamical analysis on the order of 5 35%, indicating that dynamical friction is a serious source of bias when using galaxy velocities as tracers of the underlying gravitational potential. In contrast to the literature we find that the resulting bias is not only halo mass-dependent but that the nature of the dependence changes according to the galaxy selection strategy. We make a recommendation that, in the realistic case of limited availability of spectral observations, a strictly magnitude-limited sample should be avoided to ensure an unbiased estimate of the velocity dispersion.