Galaxy Zoo: Evidence for rapid, recent quenching within a population of AGN host galaxies

TL;DR

This study analyzes the star formation histories of AGN host galaxies and inactive galaxies, revealing that some AGN hosts experienced rapid recent quenching likely driven by AGN feedback, alongside slower secular processes.

Contribution

It provides the first detailed comparison of star formation histories between Type 2 AGN hosts and inactive galaxies using Bayesian methods, highlighting the role of rapid and slow quenching mechanisms.

Findings

Some AGN hosts underwent rapid star formation quenching within the last 2 Gyr.

AGN feedback influences star formation in at least a subset of host galaxies.

Both merger-driven and secular processes contribute to galaxy and black hole co-evolution.

Abstract

We present a population study of the star formation history of 1244 Type 2 AGN host galaxies, compared to 6107 inactive galaxies. A Bayesian method is used to determine individual galaxy star formation histories, which are then collated to visualise the distribution for quenching and quenched galaxies within each population. We find evidence for some of the Type 2 AGN host galaxies having undergone a rapid drop in their star formation rate within the last 2 Gyr. AGN feedback is therefore important at least for this population of galaxies. This result is not seen for the quenching and quenched inactive galaxies whose star formation histories are dominated by the effects of downsizing at earlier epochs, a secondary effect for the AGN host galaxies. We show that histories of rapid quenching cannot account fully for the quenching of all the star formation in a galaxy's lifetime across the population of quenched AGN host galaxies, and that histories of slower quenching, attributed to secular (non-violent) evolution, are also key in their evolution. This is in agreement with recent results showing both merger-driven and non-merger processes are contributing to the co-evolution of galaxies and supermassive black holes. The availability of gas in the reservoirs of a galaxy, and its ability to be replenished, appear to be the key drivers behind this co-evolution.