Compact Groups of Galaxies in Sloan Digital Sky Survey and LAMOST Spectral Survey. II. Dynamical properties of Isolated and Embedded Groups

Yunliang Zheng, Shiyin Shen

Published 2021-02-25Version 1

Compact groups (CGs) of galaxies appear to be the densest galaxy systems containing a few luminous galaxies in close proximity to each other, which have a typical size of a few tens kilopacsec in observation. On the other hand, in the modern hierarchical structure formation paradigm, galaxies are assembled and grouped in dark matter haloes, which have a typical size of a few hundreds of kiloparsec. Few studies have explored the physical connection between the observation based CGs and halo model based galaxy groups to date. In this study, by matching the largest local CG catalog of Zheng & Shen (2020) to the halo based group catalog of Yang et al. (2007), we find that the CGs are physically heterogenous systems and can be mainly separated into two categories, the isolated systems and those embedded in rich groups or clusters. By examining the dynamical features of CGs, we find that the isolated CGs have systematically lower dynamical masses than that of non-compact ones at the same group luminosity, indicating a more evolved stage of isolated CGs. On the other hand, the embedded CGs are mixtures of chance alignments in poor clusters and recent infalling groups (sub-structures) of rich clusters.