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${}^{-1}$ < $\sigma$ < 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 $R_{sp}$. We also identified the central region of galaxy systems with a radius of $R_c$. These radii are defined by the observed integrated 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 $R_{sp}$ 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 $\log R_{sp}$ - $\log L_X$ relation has the lowest scatter. We measured $<R_{sp}>$ = $1.67\pm 0.05$~Mpc for the total sample, $<R_{sp}>$ = $1.14\pm 0.14$~Mpc for galaxy groups with $\sigma \le$ 400~km~s${}^{-1}$, $<R_{sp}>$ = $2.00\pm 0.20$~Mpc for galaxy clusters with $\sigma$ > 400~km~s${}^{-1}$. We found the average ratio of the radii $R_{sp}/R_{200c}=1.40\pm 0.02$ or $R_{sp}/R_{200m}=0.88\pm 0.02$.}

7 pages, 3 figures, 1 table