The Fastest Galaxy Evolution in an Unbiased Compact Group Sample with WISE

Abstract

We study the mid-infrared (MIR) properties of galaxies in compact groups and their environmental dependence using the Wide-field Infrared Survey Explorer (WISE) data. We use a volume-limited sample of 670 compact groups and their 2175 member galaxies with Mr < -19.77 and 0.01 < z < 0.0741, drawn from Sohn et al., which were identified using a friends-of-friends algorithm. Among the 2175 galaxies, 1541 galaxies are detected at WISE 12 mu m with a signal-to-noise ratio greater than 3. Among the 1541 galaxies, 433 AGN-host galaxies are identified by using both optical and MIR classification schemes. Using the remaining 1108 non-AGN galaxies, we find that the MIR [3.4]-[12] colors of compact group early-type galaxies are on average bluer than those of cluster early-type galaxies. When compact groups have both early-and late-type member galaxies, the MIR colors of the late-type members in those compact groups are bluer than the MIR colors of cluster late-type galaxies. As. compact groups are located in denser regions, they tend to have larger early-type galaxy fractions and bluer MIR color galaxies. These trends are also seen for neighboring galaxies around compact groups. However, compact group member galaxies always have larger early-type galaxy fractions and bluer MIR colors than their neighboring galaxies. Our findings suggest that the properties of compact group galaxies depend on both internal and external environments of compact groups, and that galaxy evolution is faster in compact groups than in the central regions of clusters.