团簇中的发光红星系团：中心占据、空间分布和偏离中心
Luminous Red Galaxies in Clusters: Central Occupation, Spatial Distributions, and Mis-centering
摘要：
来自斯隆数字巡天的发光红星系（LRG）被认为是最好理解的星系样本之一，它们被广泛用于宇宙学研究。由于它们形成了一个相对同质的群体，具有高恒星质量和红色，它们预计将以相对简单的方式占据晕。在本文中，我们研究了LRGs如何通过集群中的直接计数占据大量的晕，我们揭示了几个意想不到的趋势，表明LRGs和暗物质晕之间的连接可能不是简单的。使用redMapPer星团目录，我们推导出LRGs的中心占据作为函数丰富度Ncen（λ）。假设没有集群质量和中央星系光度之间的相关性在固定的丰富度，我们表明，集群包含一个显着较低的比例比预测的两点关联函数的中央LRG。在晕质量为10^14.5兆太阳时，我们发现Ncen=0.73，而相关研究中的Ncen为0.89。我们的中央占领功能LRG收敛到0.95在大晕群众。一个强大的反相关中心光度和集群质量在固定的丰富性需要调和我们的结果与那些基于聚类研究。我们还推导出P_BNC，最亮的星系团成员不是中央星系的概率。我们发现P_BNC约为20-30%，比Skibba等人2011年发现的值低约2倍。最后，我们研究了明亮的非中心LRGs从星系团中心的径向偏移，并表明明亮的非中心LRGs遵循不同的径向分布相比，红色的集群成员，遵循Navarro-Frank-White配置文件。这项工作表明，即使是最大质量的星系团也不总是在中心有一个LRG，而且星系团中最亮的星系也不总是中心星系。
英文摘要：
Luminous Red Galaxies (LRG) from the Sloan Digital Sky Survey are considered among the best understood samples of galaxies, and they are employed in a broad range of cosmological studies. Because they form a relatively homogeneous population, with high stellar masses and red colors, they are expected to occupy halos in a relatively simple way. In this paper, we study how LRGs occupy massive halos via direct counts in clusters and we reveal several unexpected trends suggesting that the connection between LRGs and dark matter halos may not be straightforward. Using the redMaPPer cluster catalog, we derive the central occupation of LRGs as a function richness, Ncen(λ). Assuming no correlation between cluster mass and central galaxy luminosity at fixed richness, we show that clusters contain a significantly lower fraction of central LRGs than predicted from the two-point correlation function. At halo masses of 10^14.5 Msun, we find Ncen=0.73, compared to Ncen of 0.89 from correlation studies. Our central occupation function for LRGs converges to 0.95 at large halo masses. A strong anti-correlation between central luminosity and cluster mass at fixed richness is required to reconcile our results with those based on clustering studies. We also derive P_BNC, the probability that the brightest cluster member is not the central galaxy. We find P_BNC ~ 20-30% which is a factor of ~2 lower than the value found by Skibba et al. 2011. Finally, we study the radial offsets of bright non-central LRGs from cluster centers and show that bright non-central LRGs follow a different radial distribution compared to red cluster members, which follow a Navarro-Frank-White profile. This work demonstrates that even the most massive clusters do not always have an LRG at the center, and that the brightest galaxy in a cluster is not always the central galaxy.
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