A super-linear "radio-AGN main sequence'' links mean radio-AGN power and galaxy stellar mass since z$\sim$3

TL;DR

This study reveals a super-linear relationship between mean radio-AGN power and galaxy stellar mass since z~3, indicating more massive star-forming galaxies host more active and luminous radio AGN, with implications for galaxy and black hole co-evolution.

Contribution

It introduces the concept of a 'radio-AGN main sequence' linking average radio-AGN power and galaxy mass across cosmic time, based on deep VLA-COSMOS data and AGN luminosity functions.

Findings

Radio AGN are more frequent and luminous in higher stellar mass galaxies.

The kinetic luminosity density peaks at z~2, driven mainly by galaxies with 10.5≤log(M*/M☉)<11.

A super-linear relation links mean radio-AGN power with galaxy mass, consistent with X-ray AGN trends.

Abstract

Mapping the average AGN luminosity across galaxy populations and over time encapsulates important clues on the interplay between supermassive black hole (SMBH) and galaxy growth. This paper presents the demography, mean power and cosmic evolution of radio AGN across star-forming galaxies (SFGs) of different stellar masses (${M_{*}}$). We exploit deep VLA-COSMOS 3 GHz data to build the rest-frame 1.4 GHz AGN luminosity functions at 0.1$\leq$$z$$\leq$4.5 hosted in SFGs. Splitting the AGN luminosity function into different ${M_{*}}$ bins reveals that, at all redshifts, radio AGN are both more frequent and more luminous in higher ${M_*}$ than in lower ${M_*}$ galaxies. The cumulative kinetic luminosity density exerted by radio AGN in SFGs peaks at $z$$\sim$2, and it is mostly driven by galaxies with 10.5$\leq$$\log$(${M_{*}}$/${M_{\odot}}$)$<$11. Averaging the cumulative radio AGN activity across all SFGs at each (${M_{*}}$,$z$) results in a "radio-AGN main sequence" that links the time-averaged radio-AGN power $\langle$$L_{1.4}^{{AGN}}$$\rangle$ and galaxy stellar mass, in the form: $\log$$\langle$[$L_{1.4}^{{AGN}}$/ W Hz$^{-1}]\rangle$ = (20.97$\pm$0.16) + (2.51$\pm$0.34)$\cdot$$\log$(1+$z$) + (1.41$\pm$0.09)$\cdot$($\log$[${M_{*}}$/${M_{\odot}}$] -10). The super-linear dependence on ${M_{*}}$, at fixed redshift, suggests enhanced radio-AGN activity in more massive SFGs, as compared to star formation. We ascribe this enhancement to both a higher radio AGN duty cycle and a brighter radio-AGN phase in more massive SFGs. A remarkably consistent ${M_{*}}$ dependence is seen for the evolving X-ray AGN population in SFGs. This similarity is interpreted as possibly driven by secular cold gas accretion fueling both radio and X-ray AGN activity in a similar fashion over the galaxy's lifetime.