Galaxy And Mass Assembly: the xSAGA galaxy complement in nearby galaxy groups

Abstract

ABSTRACT Groups of galaxies are the intermediate density environment in which much of the evolution of galaxies is thought to take place. In spectroscopic redshift surveys, one can identify these as close spatial-redshift associations. However, spectroscopic surveys will always be more limited in luminosity and completeness than imaging ones. Here, we combine the Galaxy And Mass Assembly (GAMA) group catalogue with the extended Satellites Around Galactic Analogues (xSAGA) catalogue of machine learning identified low-redshift satellite galaxies. We find 1825 xSAGA galaxies within the bounds of the GAMA equatorial fields (mr < 21), 1562 of which could have a counterpart in the GAMA spectroscopic catalogue (mr < 19.8). Of these, 1326 do have a GAMA counterpart with 974 below z = 0.03 (true positives) and 352 above z = 0.03 (false positives). By cross-correlating the GAMA group catalogue with the xSAGA catalogue, we can extend and characterize the satellite content of GAMA galaxy groups. We find that most groups have <5 xSAGA galaxies associated with them, but richer groups may have more. Each additional xSAGA galaxy contributes only a small fraction of the group’s total stellar mass (${\ll}10$ per cent). Selecting GAMA groups that resemble the Milky Way halo, with a few (<4) bright galaxies, we find that xSAGA can add a magnitude fainter sources to a group and that the Local Group does not stand out in the number of bright satellites. We explore the quiescent fraction of xSAGA galaxies in GAMA groups and find a good agreement with the literature.