Galaxy Zoo: the effect of bar-driven fueling on the presence of an active galactic nucleus in disc galaxies

TL;DR

This study investigates how strong bars in disc galaxies influence the presence and activity of active galactic nuclei (AGN), finding a modest but significant increase in AGN occurrence in barred galaxies after controlling for galaxy properties.

Contribution

It provides the first detailed analysis controlling for galaxy mass and colour, quantifying the contribution of bars to AGN fueling in disc galaxies.

Findings

Barred galaxies have a higher overall AGN fraction than unbarred ones.

The difference in AGN fraction persists after controlling for mass and colour, indicating a small but significant bar effect.

Barred AGN do not show stronger accretion rates than unbarred AGN at fixed properties.

Abstract

We study the influence of the presence of a strong bar in disc galaxies which host an active galactic nucleus (AGN). Using data from the Sloan Digital Sky Survey and morphological classifications from the Galaxy Zoo 2 project, we create a volume-limited sample of 19,756 disc galaxies at $0.01<z<0.05$ which have been visually examined for the presence of a bar. Within this sample, AGN host galaxies have a higher overall percentage of bars (51.8%) than inactive galaxies exhibiting central star formation (37.1%). This difference is primarily due to known effects; that the presence of both AGN and galactic bars is strongly correlated with both the stellar mass and integrated colour of the host galaxy. We control for this effect by examining the difference in AGN fraction between barred and unbarred galaxies in fixed bins of mass and colour. Once this effect is accounted for, there remains a small but statistically significant increase that represents 16% of the average barred AGN fraction. Using the $L_{\rm{[O III]}}/M_{BH} $ratio as a measure of AGN strength, we show that barred AGN do not exhibit stronger accretion than unbarred AGN at a fixed mass and colour. The data are consistent with a model in which bar-driven fueling does contribute to the probability of an actively growing black hole, but in which other dynamical mechanisms must contribute to the direct AGN fueling via smaller, non-axisymmetric perturbations.