Understanding Dual Active Galactic Nucleus Activation in the Nearby Universe

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 Swif t 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, only 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.

Was 49b: An Overmassive AGN in a Merging Dwarf Galaxy?

“…Empirically, Ellison et al (2011) find that while major mergers (M 1 /M 2 >1/3) enhance AGN activity in both galaxies, minor mergers (M 1 /M 2 <1/3) predominantly enhance AGN activity in the larger galaxy during the merger. Similarly, Koss et al (2012) find that the most powerful AGNs in minor mergers are triggered in the more massive galaxy.…”

“…Compared to other known dual AGNs, the Was49 system is highly unusual in that it is a minor merger with the more luminous AGN hosted in the secondary galaxy. In all but one of the dual AGNs with BAT detections studied by Koss et al (2012), the BAT AGN is hosted in the more massive galaxy, and the sole exception (NGC 3758) is a major merger (stellar mass ratio of 1:2).…”

Galaxy pairs in the Sloan Digital Sky Survey – VIII. The observational properties of post-merger galaxies

“…There has been considerable observational work over the last decades to confirm these theoretical predictions, which bear out many of the general, qualitative predictions of the simulations over a range of redshifts (e.g. Kennicutt et al 1987;Barton, Geller & Kenyon 2000;Kewley, Geller & Barton 2006;Woods, Geller & Barton 2006;Smith et al 2007;Jogee et al 2009;Rupke, Kewley & Chien 2010;Koss et al 2010Koss et al , 2012Silverman et al 2011;Wong et al 2011;Ramos-Almeida et al 2011, 2012Xu et al 2012;Cotini et al 2013;Lanz et al 2013). However, a full and detailed picture of the merger transformation requires large samples of galaxies that span a range in mass, mass ratio, structural properties, environments and projected separation, since all of these properties are likely to impact the specific outcome of a merger.…”

Investigation of Dual Active Nuclei, Outflows, Shock-Heated Gas, and Young Star Clusters in Markarian 266

“…For example, in a local sample of hard X-rayselected AGNs, 10% have been found to reside in dual systems with separations <100 kpc (Koss et al 2012). 34 Dual AGNs and binary AGN candidates are also being found in surveys probing to higher redshifts.…”