Morphologies of z~0.7 AGN Host Galaxies in CANDELS: No trend of merger
  incidence with AGN luminosity
  The processes that trigger Active Galactic Nuclei (AGN) remain poorly
understood. While lower luminosity AGN may be triggered by minor disturbances
to the host galaxy, stronger disturbances are likely required to trigger
luminous AGN. Major wet mergers of galaxies are ideal environments for AGN
triggering since they provide large gas supplies and galaxy scale torques.
There is however little observational evidence for a strong connection between
AGN and major mergers. We analyse the morphological properties of AGN host
galaxies as a function of AGN and host galaxy luminosity and compare them to a
carefully matched sample of control galaxies. AGN are X-ray selected in the
redshift range 0.5 < z < 0.8 and have luminosities 41 < log(L_X [erg/s]) <
44.5. 'Fake AGN' are simulated in the control galaxies by adding point sources
with the magnitude of the matched AGN. We find that AGN host and control
galaxies have comparable assymetries, Sersic indices and ellipticities at
restframe ~950nm. AGN host galaxies show neither higher average asymmetries nor
higher fractions of very disturbed objects. There is no increase in the
prevalence of merger signatures with AGN luminosity. At 95% confidence we find
that major mergers are responsible for <6% of all AGN in our sample as well as
<40% of the highest luminosity AGN log(L_X [erg/s]) ~ 43.5). Major mergers
therefore either play only a very minor role in the triggering of AGN in the
luminosity range studied or time delays are too long for merger features to
remain visible.
