Galaxy and Mass Assembly (GAMA): The Properties of Quasar Host Galaxies: Star Formation Histories and Stellar Populations

TL;DR

This study compares star formation histories and stellar populations of quasar host galaxies with normal galaxies, revealing that quasars are predominantly in star-forming galaxies with recent increased star formation, likely triggered by secular processes or minor mergers.

Contribution

It provides new insights into the star formation activity and triggering mechanisms of quasar host galaxies in the local universe.

Findings

80% of quasar hosts are star-forming on the main sequence

Quasar hosts' star formation rate increased 2-3 times in the last 100 Myr

Quasar activity likely triggered by secular processes or minor mergers

Abstract

We investigated the star formation history and stellar populations of a sample of 205 Type I quasar host galaxies (0.1$<$z$<$0.35) and compared with normal (non-active) galaxies of the same mass and redshift within the volume of the Galaxy and Mass Assembly (GAMA) redshift survey. We find that quasar host galaxies tend to be star-forming galaxies ($\sim$ 80%) lying on the star-forming MS; the fraction of quasar host galaxies that are quiescent ($\sim$ 20%) is lower than the fraction of quiescent galaxies in the comparison sample of normal galaxies (54%). We find that the mean star formation rate of quasar host galaxies has increased over the past 100 Myr by a factor of 2--3, but these galaxies were star-forming at all times previously. Our data are more consistent with quasar activity originating together with an increase in the star formation rate of otherwise normal galaxies, similar to episodic star formation in normal spirals. We argue that this indicates that secular processes and minor mergers may be the favored triggers of nuclear activity in the local Universe.