The impact of galaxy interactions on AGN activity in zCOSMOS
  Close encounters between galaxies are expected to be a viable mechanism, as
predicted by numerical simulations, by which accretion onto supermassive black
holes can be initiated. To test this scenario, we construct a sample of 562
galaxies (M*>2.5x10^10 M_sun) in kinematic pairs over the redshift range 0.25 <
z < 1.05 that are more likely to be interacting than a well-matched control
sample of 2726 galaxies not identified as being in a pair, both from the
zCOSMOS 20k spectroscopic catalog. Galaxies that harbor an active galactic
nucleus (AGN) are identified on the basis of their X-ray emission (L_x>2x10^42
erg s^-1) detected by Chandra. We find a higher fraction of AGN in galaxies in
pairs relative to isolated galaxies of similar stellar mass. Our result is
primarily due to an enhancement of AGN activity, by a factor of 1.9 (observed)
and 2.6 (intrinsic), for galaxies in pairs of projected separation less than 75
kpc and line-of-sight velocity offset less than 500 km s^-1. This study
demonstrates that close kinematic pairs are conducive environments for black
hole growth either indicating a causal physical connection or an inherent
relation, such as, to enhanced star formation. In the Appendix, we describe a
method to estimate the intrinsic fractions of galaxies (either in pairs or the
field) hosting an AGN with confidence intervals, and an excess fraction in
pairs. We estimate that 17.8_{-7.4}^{+8.4}% of all moderate-luminosity AGN
activity takes place within galaxies undergoing early stages of interaction
that leaves open the question as to what physical processes are responsible for
fueling the remaining ~80% that may include late-stage mergers.
