Understanding Dual AGN Activation in the Nearby Universe

TL;DR

This study investigates the frequency and characteristics of dual active galactic nuclei (AGN) in nearby galaxies, revealing a 10% occurrence rate and highlighting the role of galaxy mergers and luminosity in dual AGN activation.

Contribution

It provides the first comprehensive analysis of dual AGN frequency in a large, X-ray selected sample, combining multi-wavelength observations to identify new dual AGN candidates.

Findings

Dual AGN frequency at <100 kpc is 10%.

Close dual AGN (<30 kpc) are more common in luminous systems.

Dual AGN are associated with galaxy mergers and increased AGN luminosity.

Abstract

We study the fraction of dual AGN in a sample of 167 nearby (z<0.05), moderate luminosity, ultra hard X-ray selected AGN from the all-sky Swift BAT survey. Combining new Chandra and Gemini observations together with optical and X-ray observations, we find that the dual AGN frequency at scales <100 kpc is 10% (16/167). Of the 16 dual AGN, 3 (19%) were detected using X-ray spectroscopy and were not detected using emission line diagnostics. Close dual AGN (<30 kpc) tend to be more common among the most X-ray luminous systems. In dual AGN, the X-ray luminosity of both AGN increases strongly with decreasing galaxy separation, suggesting that the merging event is key in powering both AGN. 50% of the AGN with a very close companion (<15 kpc), are dual AGN. We also find that dual AGN are more likely to occur in major mergers and tend to avoid absorption line galaxies with elliptical morphologies. Finally, we find SDSS Seyferts are much less likely than BAT AGN (0.25% vs. 7.8%) to be found in dual AGN at scales <30 kpc because of a smaller number of companions galaxies, fiber collision limits, a tendency for AGN at small separations to be detected only in X-rays, and a higher fraction of dual AGN companions with increasing AGN luminosity.