2015MNRAS.450.3114B

We present the first of a series of studies of the evolution of galaxies in compact groups over the past 3 Gyr. This article focuses on the evolution of nuclear activity and how it has been affected by the dense environment of the groups. Our analysis is based on the largest multiwavelength compact-group sample to date, containing complete ultraviolet-infrared (UV-IR) photometry for 1770 isolated groups (7417 galaxies). We classified the nuclear activity of the galaxies based on optical emission-line and mid-infrared (mid-IR) diagnostic methods, as well as using spectral energy distribution fitting. We observe a 15 percent increase in the number of active galactic nucleus (AGN)-hosting late-type galaxies found in dynamically old groups over the past 3 Gyr, accompanied by a corresponding decrease in their circumnuclear star formation. Comparing our compact group results with those for local isolated field and interacting pair galaxies, we find no differences in the AGNs at the same redshift range. Based on both optical and mid-IR colour classifications, we report the absence of Seyfert 1 nuclei and attribute this to the low accretion rates caused by depletion of gas. We propose that the observed increase in low-ionization nuclear emission-line regions (LINERs) and Seyfert 2 nuclei (at low z) in early-type galaxies of dynamically young groups is due to the morphological transformation of lenticular galaxies into elliptical ones. Finally, we show that, at any given stellar mass, galaxies found in dynamically old groups are more likely to host an AGN. Our findings suggest that depletion of gas due to past star formation and tidal stripping is the major mechanism driving the evolution of nuclear activity in compact groups of galaxies.