AGN-enhanced outflows of low-ionization gas in star-forming galaxies at 1.7<z<4.6

TL;DR

This study investigates how active galactic nuclei (AGN) influence galaxy outflows at high redshift, revealing that AGN significantly boost outflow velocities in star-forming galaxies, with implications for galaxy evolution models.

Contribution

It provides the first large-sample analysis of low-ionization outflows in high-redshift AGN and compares them to star-forming galaxies, highlighting AGN's role in accelerating outflows.

Findings

AGN host galaxies exhibit higher outflow velocities than non-AGN galaxies.

Outflow velocities in AGN are similar across different X-ray luminosity bins.

High-velocity outflows are likely associated with the highly ionized phase, not the low-ionization phase.

Abstract

Fast and energetic winds are invoked by galaxy formation models as essential processes in the evolution of galaxies. These outflows can be powered either by star-formation and/or AGN activity, but the relative dominance of the two mechanisms is still under debate. We use spectroscopic stacking analysis to study the properties of the low-ionization phase of the outflow in a sample of 1330 star-forming galaxies (SFGs) and 79 X-ray detected (42<log(L_X)<45 erg/s) Type 2 AGN at 1.7<z<4.6 selected from a compilation of deep optical spectroscopic surveys, mostly zCOSMOS-Deep and VUDS. We measure mean velocity offsets of -150 km/s in the SFGs while in the AGN sample the velocity is much higher (-950 km/s), suggesting that the AGN is boosting the outflow up to velocities that could not be reached only with the star- formation contribution. The sample of X-ray AGN has on average a lower SFR than non-AGN SFGs of similar mass: this, combined with the enhanced outflow velocity in AGN hosts, is consistent with AGN feedback in action. We further divide our sample of AGN into two X-ray luminosity bins: we measure the same velocity offsets in both stacked spectra, at odds with results reported for the highly ionized phase in local AGN, suggesting that the two phases of the outflow may be mixed only up to relatively low velocities, while the highest velocities can be reached only by the highly ionized phase.