The complex relationships between AGN, bars and bulges

TL;DR

This study explores the complex interplay between active galactic nuclei (AGN), bars, and bulges in galaxies, revealing that AGN activity correlates with both bar strength and bulge prominence, independent of each other.

Contribution

It demonstrates that the correlation between AGN and bars is not solely due to bulge influence and shows a combined effect of bar strength and bulge prominence on AGN activity.

Findings

AGN fraction increases with bar strength at fixed bulge prominence.

AGN presence correlates with both bar strength and bulge prominence.

Controlling for bulge prominence does not eliminate the AGN-bar relationship.

Abstract

Context. Via scaling relations, it is well-known that active galactic nuclei (AGN) and bulges are linked. This link was thought to be driven by mergers, but recent studies show that secular processes are the dominant mechanism of supermassive black hole growth. One such secular mechanism is gas inflow driven by large-scale bars. Since bulges can also grow via these bars, there is likely some common process between these three features. Aims. We investigate whether the observed correlation between AGN and bars is real or arises as a result of correlations between bars and bulges. Methods. Using a catalogue of AGN identifications and galaxy morphologies in the DESI Legacy Survey at $z\leq0.1$, we control for mass and colour and investigate the AGN fraction variation with bulge prominence and bar strength. Results. We first show that the variation in AGN fraction between strongly barred, weakly barred and unbarred galaxies does not qualitatively change if we additionally control for bulge prominence. Second, we find that in fixed bins of bulge prominence, the AGN fraction increases with increasing bar strength. In subsamples split by bar strength, the AGN fraction increases with bulge prominence, indicating that AGN presence correlates with both bar strength and bulge prominence simultaneously.