ZFOURGE catalogue of AGN candidates: an enhancement of 160{\mu}m-derived star-formation rates in active galaxies to $z$ = 3.2

TL;DR

This study examines how active galactic nuclei influence star formation in their host galaxies up to redshift 3.2, revealing that infrared-selected AGN are associated with significantly higher star-formation rates, challenging previous assumptions about AGN quenching.

Contribution

It provides a comprehensive analysis of AGN host galaxy star formation across multiple wavelengths, highlighting the differential impact of IR and X-ray selected AGN on star formation activity.

Findings

Infrared-selected AGN hosts show up to 5 times higher sSFR than inactive galaxies.

X-ray AGN hosts are mostly similar to inactive galaxies in star formation.

AGN are less associated with quiescent galaxies than previously thought.

Abstract

We investigate active galactic nuclei (AGN) candidates within the FourStar Galaxy Evolution Survey (ZFOURGE) to determine the impact they have on star-formation in their host galaxies. We first identify a population of radio, X-ray, and infrared-selected AGN by cross-matching the deep $K_{s}$-band imaging of ZFOURGE with overlapping multi-wavelength data. From this, we construct a mass-complete (log(M$_{*}$/M$_{\odot}$) $\ge$ 9.75), AGN luminosity limited sample of 235 AGN hosts over z = 0.2 - 3.2. We compare the rest-frame U - V versus V - J (UVJ) colours and specific star-formation rates (sSFRs) of the AGN hosts to a mass-matched control sample of inactive (non-AGN) galaxies. UVJ diagnostics reveal AGN tend to be hosted in a lower fraction of quiescent galaxies and a higher fraction of dusty galaxies than the control sample. Using 160{\mu}m Herschel PACS data, we find the mean specific star-formation rate of AGN hosts to be elevated by 0.34$\pm$0.07 dex with respect to the control sample across all redshifts. This offset is primarily driven by infrared-selected AGN, where the mean sSFR is found to be elevated by as much as a factor of ~5. The remaining population, comprised predominantly of X-ray AGN hosts, is found mostly consistent with inactive galaxies, exhibiting only a marginal elevation. We discuss scenarios that may explain these findings and postulate that AGN are less likely to be a dominant mechanism for moderating galaxy growth via quenching than has previously been suggested.