Catalogs of Compact Groups of Galaxies from the Enhanced SDSS DR12

TL;DR

This paper presents a large, enhanced catalog of compact galaxy groups from SDSS DR12, covering a broad redshift range and including detailed properties, enabling studies of galaxy interactions over cosmic time.

Contribution

It introduces a significantly expanded and deeper catalog of compact galaxy groups using a friends-of-friends algorithm, including volume-limited samples and without the isolation criterion.

Findings

Catalog contains 1588 groups with 5179 galaxies.

Groups with low velocity dispersion show signs of ongoing interactions.

Number density decreases with increasing redshift.

Abstract

We apply a friends-of-friends algorithm to an enhanced SDSS DR12 spectroscopic catalog including redshift from literature to construct a catalog of $1588~N\ge3$ compact groups of galaxies containing 5179 member galaxies and covering the redshift range $0.01 < z < 0.19$. This catalog contains 18 times as many systems and reaches 3 times the depth of similar catalog of Barton et al. (1996). We construct catalogs from both magnitude-limited and volume-limited galaxy samples. Like Barton et al. (1996) we omit the frequently applied isolation criterion in the compact group selection algorithm. Thus the groups selected by fixed projected spatial and rest frame line-of-sight velocity separation produce a catalog of groups with a redshift independent median size. In contrast with previous catalogs, the enhanced SDSS DR12 catalog (including galaxies with $r < 14.5$) includes many systems with $z\leq 0.05$. The volume-limited samples are unique to this study. The compact group candidates in these samples have a median stellar mass independent of redshift. Groups with velocity dispersion $\leq 100$ km s$^{-1}$ show abundant evidence for ongoing dynamical interactions among the members. The number density of the volume-limited catalogs agrees with previous catalogs at the lowest redshifts but decreases as the redshift increases. The SDSS fiber placement constraints limit the catalog completeness. In spite of this issue the volume-limited catalogs provide a promising basis for detailed spatially resolved probes of the impact of galaxy-galaxy interactions within similar dense systems over a broad redshift range.