Title: Alignment of Brightest Cluster Galaxies with their Host Clusters Show Chinese title

Title: 最亮团星系与其宿主星团的 alignments

Abstract: We examine the alignment between Brightest Cluster Galaxies (BCGs) and their host clusters in a sample of 7031 clusters with 0.08<z<0.44 found using a matched-filter algorithm and an independent sample of 5744 clusters with 0.1<z<0.3 selected with the maxBCG algorithm, both extracted from the Sloan Digital Sky Survey Data Release 6 imaging data. We confirm that BCGs are preferentially aligned with the cluster's major axis; clusters with dominant BCGs (>0.65 mag brighter than the mean of the second and third ranked galaxies) show stronger alignment than do clusters with less dominant BCGs at the 4.4 sigma level. Rich clusters show a stronger alignment than do poor clusters at the 2.3 sigma level. Low redshift clusters (z<0.26) show more alignment than do high redshift (z>0.26) clusters, with a difference significant at the 3.0 sigma level. Our results do not depend on the algorithm used to select the cluster sample, suggesting that they are not biased by systematics of either algorithm. The correlation between BCG dominance and cluster alignment may be a consequence of the hierarchical merging process which forms the cluster. The observed redshift evolution may follow from secondary infall at late redshifts. Show Chinese abstract

Abstract: 我们研究了使用匹配滤波算法发现的包含7031个红移范围为0.08到0.44的星系团样本以及独立选择的由maxBCG算法选出的红移范围为0.1到0.3的5744个星系团样本（这两个样本均来自斯隆数字巡天数据发布6代成像数据）中，最亮团簇星系(BCGs)与其宿主星系团之间的对齐情况。 我们确认BCGs倾向于与星系团的主要轴线对齐；主导BCGs（比第二和第三亮星系的平均亮度亮0.65等以上）的星系团显示出比非主导BCGs的星系团更强的对齐，这种差异在4.4倍标准差水平上显著。富集星系团在2.3倍标准差水平上表现出比贫瘠星系团更强的对齐。 低红移星系团(z<0.26)比高红移(z>0.26)星系团显示出更多的对齐，这种差异在3.0倍标准差水平上显著。我们的结果不受用于选择星系团样本的算法的影响，表明它们没有受到两种算法系统性的偏差影响。 BCGs优势与星系团对齐之间的相关性可能是由于形成星系团的等级合并过程的结果。观测到的红移演化可能源于晚近的次级吸积。