标题： LoCuSS：将最亮星系团星系的主导性和形状与大质量星系团的形成历史相联系 显示英文标题

标题： LoCuSS: Connecting the Dominance and Shape of Brightest Cluster Galaxies with the Assembly History of Massive Clusters

摘要： 我们研究了59个大质量星系团样本中排名第一和第二的星系之间的光度差距dm12，使用的数据来自海尔望远镜、哈勃望远镜、钱德拉和斯皮策。 我们发现dm12分布p(dm12)是dm12的递减函数，我们将其拟合为一条直线：p(dm12)与-(0.13±0.02)dm12成正比。 具有“大”光度差距的星系团比例为p(dm12≥1)=0.37±0.08，这比通过匹配星系团平均光度函数的Schechter函数蒙特卡罗模拟得到的结果高出3sigma。 我们还识别出四个具有“极端”光度差距的星系团，dm12≥2，给出的比例为p(dm12≥2)=0.07+0.05-0.03。 更一般地说，大光度差距星系团相对同质，具有椭圆/盘状最亮星系（BCGs），尖锐的气体密度分布（即强冷却核心），高浓度和低子结构分数。 相反，小光度差距星系团是异质的，涵盖了从箱状/椭圆/盘状BCG形态的全部范围，冷却核心强度和暗物质浓度的全部范围，并且有大的子结构分数。 综合来看，这些结果表明光度差距的幅度是集群形成时期和最近吸积历史的函数。 因此，“BCG主导”是集群可能经历的一个阶段，而不是进化的“死胡同”。 我们还将我们的结果与基于Millennium Simulation的半解析模型预测进行了比较。 没有任何模型能够再现所有观测结果，这强调了当前模型在匹配BCGs的经验特性方面的不足。 我们确定了AGN反馈的强度以及每个模型中星系在与BCG合并后被补充的效率可能是这些差异的可能原因。 [摘要] 显示英文摘要

摘要： We study the luminosity gap, dm12, between the first and second ranked galaxies in a sample of 59 massive galaxy clusters, using data from the Hale Telescope, HST, Chandra, and Spitzer. We find that the dm12 distribution, p(dm12), is a declining function of dm12, to which we fitted a straight line: p(dm12) propto -(0.13+/-0.02)dm12. The fraction of clusters with "large" luminosity gaps is p(dm12>=1)=0.37+/-0.08, which represents a 3sigma excess over that obtained from Monte Carlo simulations of a Schechter function that matches the mean cluster galaxy luminosity function. We also identify four clusters with "extreme" luminosity gaps, dm12>=2, giving a fraction of p(dm12>=2)=0.07+0.05-0.03. More generally, large luminosity gap clusters are relatively homogeneous, with elliptical/disky brightest cluster galaxies (BCGs), cuspy gas density profiles (i.e. strong cool cores), high concentrations, and low substructure fractions. In contrast, small luminosity gap clusters are heterogeneous, spanning the full range of boxy/elliptical/disky BCG morphologies, the full range of cool core strengths and dark matter concentrations, and have large substructure fractions. Taken together, these results imply that the amplitude of the luminosity gap is a function of both the formation epoch, and the recent infall history of the cluster. "BCG dominance" is therefore a phase that a cluster may evolve through, and is not an evolutionary "cul-de-sac". We also compare our results with semi-analytic model predictions based on the Millennium Simulation. None of the models are able to reproduce all of the observational results, underlining the inability of current models to match the empirical properties of BCGs. We identify the strength of AGN feedback and the efficiency with which cluster galaxies are replenished after they merge with the BCG in each model as possible causes of these discrepancies. [Abridged]