The splashback radius of groups and clusters of galaxies at low redshifts

Abstract

We present a study of the distribution of galaxies along the radius of 157 groups and clusters of galaxies (200 km s−1 < σ < 1100 km s−1) of the local Universe (0.01 < z < 0.1). We introduced a new boundary of galaxy systems and identified it with the splashback radius Rsp. We also identified the central region of galaxy systems with a radius of Rc. These radii are defined by the observed integral distribution of the total number of galaxies depending on the squared distance from the center of the groups/clusters coinciding, as a rule, with the brightest galaxy. We show that the radius Rsp is proportional to the R200c (radius of the virialized region of a galaxy cluster) and to the radius of the central region Rc with a slope close to 1. Among the obtained dependences of the radii on X-ray luminosity, the log Rsp - log Lx relation has the lowest scatter. We measured < Rsp > = 1.67 ± 0.05 Mpc for the total sample, < Rsp > = 1.14 ± 0.14 Mpc for galaxy groups with σ ≤ 400 km s−1, < Rsp > = 2.00 ± 0.20 Mpc for galaxy clusters with σ > 400 km s−1. We found the average ratio of the radii Rsp/R200c = 1.40 ± 0.02 or Rsp/R200m = 0.88 ± 0.02.