Active Galactic Nuclei Abundance in Cosmic Voids
  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.
