Radio Loud AGNs are Mergers
  We measure the merger fraction of Type 2 radio-loud and radio-quiet active
galactic nuclei at z>1 using new samples. The objects have HST images taken
with WFC3 in the IR channel. These samples are compared to the 3CR sample of
radio galaxies at z>1 and to a sample of non-active galaxies. We also consider
lower redshift radio galaxies with HST observations and previous generation
instruments (NICMOS and WFPC2). The full sample spans an unprecedented range in
both redshift and AGN luminosity. We perform statistical tests to determine
whether the different samples are differently associated with mergers. We find
that all (92%) radio-loud galaxies at z>1 are associated with recent or ongoing
merger events. Among the radio-loud population there is no evidence for any
dependence of the merger fraction on either redshift or AGN power. For the
matched radio-quiet samples, only 38% are merging systems. The merger fraction
for the sample of non-active galaxies at z>1 is indistinguishable from
radio-quiet objects. This is strong evidence that mergers are the triggering
mechanism for the radio-loud AGN phenomenon and the launching of relativistic
jets from supermassive black holes. We speculate that major BH-BH mergers play
a major role in spinning up the central supermassive black holes in these
objects.
