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 𝑅 𝑠 𝑝 . We also identified the central region of galaxy systems with a radius of 𝑅 𝑐 . 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 𝑅 𝑠 𝑝 is proportional to the 𝑅 200𝑐 (radius of the virialized region of a galaxy cluster) and to the radius of the central region 𝑅 𝑐 with a slope close to 1. Among the obtained dependences of the radii on X-ray luminosity, the log 𝑅 𝑠 𝑝 -log 𝐿 𝑋 relation has the lowest scatter. We measured < 𝑅 𝑠 𝑝 > = 1.67 ± 0.05 Mpc for the total sample, < 𝑅 𝑠 𝑝 > = 1.14 ± 0.14 Mpc for galaxy groups with 𝜎 ≤ 400 km s −1 , < 𝑅 𝑠 𝑝 > = 2.00 ± 0.20 Mpc for galaxy clusters with 𝜎 > 400 km s −1 . We found the average ratio of the radii 𝑅 𝑠 𝑝 /𝑅 200𝑐 = 1.40 ± 0.02 or 𝑅 𝑠 𝑝 /𝑅 200𝑚 = 0.88 ± 0.02.