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

TL;DR

This study investigates the star formation histories and stellar populations of 205 low-redshift Type I quasar host galaxies by comparing them to a mass- and redshift-matched sample of normal galaxies within the GAMA survey, using SED analyses to derive SF properties. The quasar hosts are found to be predominantly star-forming, with a minority that are quiescent, and the mean SFR has risen by a factor of $2$--$3$ in the last $\sim$100 Myr, consistent with episodic SF accompanying AGN activity. The results support a scenario where secular processes and minor mergers trigger nuclear activity and co-evolve with star formation rather than quenching it, at least in the local Universe. The study minimizes selection biases by matching samples within the same survey volume and applying consistent SFH derivations across AGN hosts and control galaxies.

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.

Figures (1)

• Figure 1: (a) Distribution of bolometric luminosities for quasars derived from cigale fits. This excludes 8 quasars (3.9 % of quasar sample) where cigale did not return a quasar luminosity. (b) Distribution of absolute SDSS $i$ band magnitude ($k$-corrected and extinction corrected based on GAMA survey data).