The environments of z~1 Active Galactic Nuclei at 3.6um
  We present an analysis of a large sample of AGN environments at z~1 using
stacked Spitzer data at 3.6um. The sample contains type-1 and type-2 AGN in the
form of quasars and radio galaxies, and spans a large range in both optical and
radio luminosity. We find, on average, that 2 to 3 massive galaxies containing
a substantial evolved stellar population lie within a 200-300 kpc radius of the
AGN, constituting a >8-sigma excess relative to the field. Secondly, we find
evidence for the environmental source density to increase with the radio
luminosity of AGN, but not with black-hole mass. This is shown first by
dividing the AGN into their classical AGN types, where we see more significant
over-densities in the fields of the radio-loud AGN. If instead we dispense with
the classical AGN definitions, we find that the source over-density as a
function of radio luminosity for all our AGN exhibits a positive correlation.
One interpretation of this result is that the Mpc-scale environment is in some
way influencing the radio emission that we observe from AGN. This could be
explained by the confinement of radio jets in dense environments leading to
enhanced radio emission or, alternatively, may be linked to more rapid
black-hole spin brought on by galaxy mergers.
