Shapes of galaxies hosting radio-loud AGNs with z \leq 1

TL;DR

This study investigates the shapes of galaxies hosting radio-loud AGNs up to redshift 1, revealing evolution in host galaxy morphology with luminosity and redshift, and suggesting a consistent link between AGN activity and galaxy shape over cosmic time.

Contribution

It provides new insights into the morphological evolution of RLAGN host galaxies and their relation to radio luminosity across redshifts up to 1.

Findings

High-luminosity RLAGNs at z~1 have more elongated hosts than local counterparts.

The shape distribution of RLAGN hosts evolves with redshift and luminosity.

Radio luminosity evolution can explain the observed morphological changes.

Abstract

Links between the properties of radio-loud active galactic nuclei (RLAGNs) and the morphology of their hosts may provide important clues for our understanding of how RLAGNs are triggered. In this work, focusing on passive galaxies, we study the shape of the hosts of RLAGNs selected from the Karl G. Jansky Very Large Array Cosmic Evolution Survey (VLA-COSMOS) 3GHz Large Project, and compare them with previous results based on the first data release (DR1) of the LOFAR Two-Metre Sky Survey (LoTSS). We find that, at redshifts of between 0.6 and 1, high-luminosity ($L_{1.4 GHz}\gtrsim10^{24}\rm W Hz^{-1}$) RLAGNs have a wider range of optical projected axis ratios than their low-redshift counterparts, which are essentially all found in round galaxies with axis ratios of higher than 0.7. We construct control samples and show that although the hosts of high-redshift RLAGNs with the highest luminosities still have a rounder shape compared with the non-RLAGNs, they on average have a smaller axis ratio (more elongated) than the local RLAGNs with similar stellar masses and radio luminosities. This evolution can be interpreted as a byproduct of radio luminosity evolution, namely that galaxies at fixed stellar mass are more radio luminous at high redshifts: artificially increasing the radio luminosities of local galaxies ($z\leq$0.3) by a factor of 2 to 4 can remove the observed evolution of the axis ratio distribution. If this interpretation is correct then the implication is that the link between AGN radio luminosity and host galaxy shape is similar at $z\simeq1$ to in the present-day Universe.