INDIVIDUAL AND GROUP GALAXIES IN CNOC1 CLUSTERS
INDIVIDUAL AND GROUP GALAXIES IN CNOC1 CLUSTERS
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DOI：
10.1088/0004-637x/698/1/83
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发表时间：
2009-04
期刊：
影响因子：
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通讯作者：
I. Li;H. Yee;E. Ellingson
中科院分区：
文献类型：
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作者：
I. Li;H. Yee;E. Ellingson
利用来自加拿大观测宇宙学巡天网络的16个中间红移（0.17 < z < 0.55）星系团的宽视场BVRcI成像，研究了星系团星系群及其演化对环境的依赖关系。使用经验光度红移技术估计星系光度红移，并使用改进的朋友-朋友算法在光度红移空间中识别星系群。我们利用红色星系分数（fred）来推断星系团中星系的演化状态，既使用单个星系，也使用群星系。我们使用了本地星系密度Σ5，它是用第五近邻距离推导出来的，作为本地环境的度量，而星团中心半径rCL，作为全球星团环境的代理。我们的星团样本在亮度选择和恒星质量选择样本中都表现出布彻-奥姆勒效应。我们发现fred强烈依赖于Σ5和rCL，并且在所有Σ5和rCL箱子中都观察到Butcher-Oemler效应。然而，当星系团星系被分成rCL仓，或分成群亚样本和非群亚样本时，对局域星系密度的依赖性就会减弱。这表明星系所处的暗物质晕的特性对星系的数量和进化历史有着重要的影响。我们发现我们的数据与位于连续丰富的群体（即更大质量的暗物质晕）的星系团在早期红移时达到高fred值的情景一致。与此相关的是，我们观察到一个清晰的“预处理”特征，在这个特征中，属于中等质量的落入星系群的星系团星系比那些被归类为非星系团星系的星系团星系表现出更强的演化，尤其是在星系团的外围。这一结果表明，星系群落入星系团是造成布彻-欧姆勒效应的重要因素。
Using wide-field BVRcI imaging for a sample of 16 intermediate redshift (0.17 < z < 0.55) galaxy clusters from the Canadian Network for Observational Cosmology Survey, we investigate the dependence of cluster galaxy populations and their evolution on environment. Galaxy photometric redshifts are estimated using an empirical photometric redshift technique and galaxy groups are identified using a modified friends-of-friends algorithm in photometric redshift space. We utilize the red galaxy fraction (fred) to infer the evolutionary status of galaxies in clusters, using both individual galaxies and galaxies in groups. We apply the local galaxy density, Σ5, derived using the fifth nearest neighbor distance, as a measure of local environment, and the cluster-centric radius, rCL, as a proxy for global cluster environment. Our cluster sample exhibits a Butcher–Oemler effect in both luminosity-selected and stellar-mass-selected samples. We find that fred depends strongly on Σ5 and rCL, and the Butcher–Oemler effect is observed in all Σ5 and rCL bins. However, when the cluster galaxies are separated into rCL bins, or into group and nongroup subsamples, the dependence on local galaxy density becomes much weaker. This suggests that the properties of the dark matter halo in which the galaxy resides have a dominant effect on its galaxy population and evolutionary history. We find that our data are consistent with the scenario that cluster galaxies situated in successively richer groups (i.e., more massive dark matter halos) reach a high fred value at earlier redshifts. Associated with this, we observe a clear signature of “preprocessing,” in which cluster galaxies belonging to moderately massive infalling galaxy groups show a much stronger evolution in fred than those classified as nongroup galaxies, especially at the outskirts of the cluster. This result suggests that galaxies in groups infalling into clusters are significant contributors to the Butcher–Oemler effect.