Evolution of the Most Massive Galaxies to z ~ 0.6: II. The link between radio AGN activity and star formation

TL;DR

This study investigates the relationship between radio AGN activity and recent star formation in massive galaxies at z~0.2 and z~0.6, revealing cyclical activity patterns and evolution of emission properties over cosmic time.

Contribution

It provides new insights into how radio AGN activity correlates with star formation history and how these processes evolve with redshift in massive galaxies.

Findings

Radio-loud and radio-quiet galaxies have similar recent star formation fractions.

Star formation often occurs as a burst in massive galaxies.

Radio and emission-line luminosities evolve significantly with redshift.

Abstract

We analyze the optical spectra of massive (log M*/Msun > 11.4) radio-loud galaxies at z~0.2 and z~0.6. By comparing stellar population parameters of these radio-loud samples with radio-quiet control samples, we investigate how the presence of a radio-emitting jet relates to the recent star formation history of the host galaxy. We also investigate how the emission-line properties of the radio galaxies evolve with redshift by stacking their spectra. Our main results are the following. (1) Both at low and at high redshift, half as many radio-loud as radio-quiet galaxies have experienced significant star formation in the past Gyr. (2) The Balmer absorption line properties of massive galaxies that have experienced recent star formation show that star formation occurred as a burst in many of these systems. (3) Both the radio and the emission-line luminosity of radio AGN evolve significantly with redshift. However, radio galaxies with similar stellar population parameters, have similar emission-line properties both at high- and at low-redshift. These results suggest that massive galaxies experience cyclical episodes of gas accretion, star formation and black hole growth, followed by the production of a radio jet that shuts down further activity. The behaviour of galaxies with log M*/Msun > 11.4 is the same at z = 0.6 as it is at z = 0.2, except that higher redshift galaxies experience more star formation and black hole growth and produce more luminous radio jets during each accretion cycle.