Active Galactic Nuclei Abundance in Cosmic Voids

Abstract

The abundance of active galactic nuclei (AGN) in cosmic voids is relatively unexplored in the literature, but can potentially provide new constraints on the environmental dependence of AGN activity and the AGN-host co-evolution. We investigated AGN fraction in one of the largest samples of optically selected cosmic voids from SDSS Data Release 12 for redshift range 0.2-0.7 for moderately bright and bright AGN. We separated inner and outer void regions based on the void size, given by its effective void radius. We classified galaxies at a distance < 0.6Reff as inner void members and galaxies in the interval 0.6 < R/Reff < 1.3 as outer void galaxies. We found higher average fractions in the inner voids (4.9+-0.7)% than for their outer counterparts (3.1+-0.1)% at z>0.42, which clearly indicates an environmental dependence. This conclusion was confirmed upon further separating the data in narrower void-centric distance bins and measured a significant decrease in AGN activity from inner to outer voids for z>0.42. At low redshifts (z<0.42), we find very weak dependence on the environment for the inner and outer regions for two out of three bins. We argue that the higher fraction in low-density regions close to void centers relative to their outer counterparts observed in the two higher redshift bins suggests that there may occur more efficient galaxy interactions at one-to-one level in voids which may be suppressed in denser environments due to higher velocity dispersions. It could also indicate less prominent ram pressure stripping in voids or some intrinsic host or void environment properties.

11 pages, 3 figures

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