The Relationship of Active Galactic Nuclei & Quasars With Their Local
  Galaxy Environment
  We explore how the local environment is related to properties of active
galactic nuclei (AGNs) of various luminosities. Recent simulations and
observations are converging on the view that the extreme luminosity of quasars,
the brightest of AGNs, is fueled in major mergers of gas-rich galaxies. In such
a picture, quasars, the highest luminosity AGNs, are expected to be located in
regions with a higher density of galaxies on small scales where mergers are
more likely to take place. However, in this picture, the activity observed in
low-luminosity AGNs is due to secular processes that are less dependent on the
local galaxy density. To test this hypothesis, we compare the local photometric
galaxy density on kiloparsec scales around spectroscopic type I and type II
quasars to the local density around lower-luminosity spectroscopic type I and
type II AGNs. To minimize projection effects and evolution in the photometric
galaxy sample we use to characterize AGN environments, we place our random
control sample at the same redshift as our AGNs and impose a narrow redshift
window around both the AGNs and control targets. Our results support these
merger models for bright AGN origins. We find that the brightest sources have
overdensities that increase on the smallest scales compared to dimmer sources.
In addition, we investigate the nature of the quasar and AGN environments
themselves and find that the increased overdensity of early-type galaxies in
the environments of bright type I sources suggests that they are located in
richer cluster environments than dim sources. We measure increased environment
overdensity with increased quasar black hole mass, consistent with the
well-known M_{DMH}-M_{BH} relationship, and find evidence for quenching in the
environments of high accretion efficiency type I quasars.
