BL Lac对象的聚类环境RGB 1745+398
Clustering environment of BL Lac object RGB 1745+398
摘要：
BL Lac天体RGB 1745+398位于一个环境中，使得有可能比其他BL Lac天体的环境更深入地研究它周围的星团。以BL Lac为中心的星团就像一个强大的引力透镜，在其周围形成一个巨大的弧形。为了更准确地研究该天体所处的环境和特征，我们利用吸收谱线测量了该星系团中星系的红移。然后从红移中得到速度色散。利用引力透镜测量星团中心的质量。然后，可以使用软化的等温球质量分布来估计整个团簇的质量。最后，通过计算BL Lac天体附近的星系数量并获得星系-BL Lac空间协方差函数$B_{gb}$来确定星系团的丰富度。观测到的9个星系的红移接近BL Lac天体的红移，证实了星系团的存在。星团的平均红移为0.268，速度色散为$(470^{+190}_{-110})$ km s $^{-1}$ .星团的质量是$M_{500}=(4^{+3}_{-2})\times10^{14} M_{\sun}$，这意味着一个相当大的星团。丰富度测量也表明这是一个丰富的集群：协方差函数的结果是$B_{gb}=(600\pm200)$ Mpc $^{1.77}$，这对应于阿贝尔丰富度类1，这是一致的质量和速度分散的集群。
英文摘要：
The BL Lac object RGB 1745+398 lies in an environment that makes it possible to study the cluster around it more deeply than the environments of other BL Lac objects. The cluster centered on the BL Lac works as a strong gravitational lens, forming a large arc around itself. The aim of this paper is to study the environment and characteristics of this object more accurately than the environments of other BL Lac objects have been before.We measured the redshifts of galaxies in the cluster from the absorption lines in their spectra. The velocity dispersion was then obtained from the redshifts. The gravitational lensing was used for measuring the mass at the center of the cluster. The mass of the whole cluster could then be estimated using the softened isothermal sphere mass distribution. Finally, the richness of the cluster was determined by counting the number of galaxies near the BL Lac object and obtaining the galaxy-BL Lac spatial covariance function, $B_{gb}$. The redshifts of nine galaxies in the field were measured to be near the redshift of the BL Lac object, confirming the presence of a cluster. The average redshift of the cluster is 0.268, and the velocity dispersion $(470^{+190}_{-110})$ km s$^{-1}$. The mass of the cluster is $M_{500}=(4^{+3}_{-2})\times10^{14} M_{\sun}$ which implies a rather massive cluster. The richness measurement also suggests that this is a rich cluster: the result for covariance function is $B_{gb}=(600\pm200)$ Mpc$^{1.77}$, which corresponds to Abell richness class 1 and which is consistent with the mass and velocity dispersion of the cluster.
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