The properties of radio and mid-infrared detected galaxies and the effect of environment on the co-evolution of AGN and star formation at z ∼ 1

Abstract

ABSTRACT In this study, we investigate 179 radio-infrared (IR) galaxies drawn from a sample of spectroscopically confirmed galaxies, which are detected in radio and mid-IR (MIR) in the redshift range of 0.55 ≤ z ≤ 1.30 in the Observations of Redshift Evolution in Large Scale Environments (ORELSE) survey. We constrain the active galactic nuclei (AGN) contribution to the total IR luminosity (fAGN), and estimate the AGN luminosity (LAGN) and the star formation rate (SFR). Based on the fAGN and radio luminosity, radio–IR galaxies are split into galaxies that host either high- or low-fAGN AGN (high-/low-fAGN), and star-forming galaxies (SFGs) with little to no AGN activity. We study the properties of the three radio–IR sub-samples comparing to an underlying parent sample. In the comparison of radio luminosity of three sub-samples, no significant difference was found, which could be due to the combined contribution of radio emission from AGN and star formation. We find a positive relationship between LAGN and specific SFR (sSFR) for both AGN sub-samples, strongly suggesting a co-evolution scenario of AGN and SF in these galaxies. A toy model is designed to demonstrate this co-evolution scenario, where we find that, in almost all cases, a rapid quenching time-scale is required, which we argue is a signature of AGN quenching. The environmental preference for intermediate/infall regions of clusters/groups remains across the co-evolution scenario, which suggests that galaxies might be in an orbital motion around the cluster/group during the scenario.