Photometric variability in star-forming galaxies as evidence for low-mass AGN and a precursor to quenching

TL;DR

This study uses optical variability measurements of low-redshift galaxies to explore the connection between black hole activity and galaxy evolution, revealing variability as an early indicator of AGN activity and galaxy quenching.

Contribution

It demonstrates that optical variability can serve as an effective tracer for low-mass AGNs and their role in galaxy evolution, especially as a precursor to star-formation quenching.

Findings

Higher variability in star-forming galaxies below 10^11 M_sun.

Peak variability in galaxies with specific star-formation rates between -11 and -10.

Variability indicates black hole growth precedes star-formation decline.

Abstract

We measure the optical variability in $\sim$ 16500 low-redshift (z $\sim$ 0.1) galaxies to map the relations between AGN activity and galaxy stellar mass, specific star-formation rate, half-light radius and bulge-to-total ratio. To do this, we use a reduced $\chi ^2$ variability measure on > 10 epoch lightcurves from the Zwicky Transient Facility and combine with spectroscopic data and derived galaxy parameters from the Sloan Digital Sky Survey. We find that below stellar mass of $10^{11} M_\odot$, galaxies classed as star-forming via the BPT diagram have higher mean variabilities than AGN or composite galaxies. Revealingly, the highest mean variabilities occur in star-forming galaxies in a narrow range of specific star-formation, $-11<\log($sSFR/yr$^{-1})<-10$. In very actively star-forming galaxies $(\log($sSFR/yr$^{-1})>-10)$, the reduced variability implies a lack of instantaneous correlation with star-formation rate. Our results may indicate that a high level of variability, and thus black hole growth, acts as a precursor for reduced star-formation, bulge growth, and revealed AGN-like emission lines. These results add to the mounting evidence that optical variability can act as a viable tracer for low-mass AGNs and that such AGNs can strongly affect their host galaxy.