We counted galaxies in the area with 10 Mpc radius around 30 isolated ACO clusters at redshifts z < 0.1. We show that surface densities of galaxies around clusters regularly decrease till 10 Mpc. Separate counts of blue and red galaxies of the cluster environment revealed that at all cluster-centric distances the surface density of red galaxies are higher than that of blue ones. The surface density of red galaxies decrease significantly with increase of distance from the cluster. Meanwhile, the decrease of the surface density of blue galaxies is very smooth and is almost not noticeable at higher cluster-centric distances. It is suggested that the red population of the cluster environment consists of backsplash galaxies that form the cluster halo, which is extended farther than 10 Mpc from the cluster center. The blue population consists mainly of the field galaxies. The velocity dispersion of blue galaxies in the cluster environment is higher than the velocity dispersion of red galaxies, which is evidences of their different entities. The mass of the halo is comparable to the cluster mass.

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关于星系团的大小和质量

我们在红移 z < 0.1 处对 30 个孤立的 ACO 星团周围半径为 10 Mpc 的区域中的星系进行了计数。我们表明星团周围星系的表面密度有规律地降低到 10 Mpc。对星团环境中蓝色和红色星系的单独计数表明，在所有以星团为中心的距离上，红色星系的表面密度都高于蓝色星系的表面密度。红色星系的表面密度随着与星团距离的增加而显着降低。同时，蓝色星系表面密度的降低非常平滑，并且在更高的星团中心距离下几乎不明显。建议星团环境的红色种群由形成星团晕的后溅星系组成，该星团从星团中心延伸超过 10 Mpc。蓝色族群主要由场星系组成。团簇环境中蓝色星系的速度弥散高于红色星系的速度弥散，这是它们不同实体的证据。晕的质量与星团质量相当。