Hosts and triggers of AGNs in the Local Universe
  Based on the spectroscopic and shear catalogs for SDSS galaxies in the local
Universe, we compare optically-selected active galactic nuclei (AGNs) with
control star-forming and quiescent galaxies on galactic, inter-halo and larger
scales. We find that AGNs are preferentially found in two specific stages of
galaxy evolution: star-burst and `green valley' phases, and that the stellar
population of their host galaxies is quite independent of stellar mass,
different from normal galaxies. Combining galaxy-galaxy lensing and galaxy
clustering on large scales, we measure the mass of AGN host halos. The typical
halo mass is about $10^{12}h^{-1}\rm M_{\odot}$, similar to the characteristic
mass in the stellar mass-halo mass relation (SHMR). For given stellar mass, AGN
host galaxies and star-forming galaxies share the same SHMR, while quiescent
galaxies have more massive halos. Clustering analysis on halo scales reveals
that AGNs are surrounded by a larger number of satellites (with stellar mass
down to 1/1000 of the mass of the central galaxy) than star-forming galaxies,
and that galaxies with larger stellar velocity dispersion have more satellites.
The number of satellites also increase with halo mass, reaching unity around
$10^{12}h^{-1}\rm M_{\odot}$. Our results suggest a scenario, in which the
interaction of the central galaxy with the satellites triggers an early episode
of star burst and AGN activities, followed by multiple AGN cycles driven by the
non-axisymmetric structure produced by the interaction. The feedback from the
starburst and AGN reduces the amount of cold gas for fueling the central black
hole, producing a characteristic halo mass scale, $\sim 10^{12}h^{-1}\rm
M_{\odot}$, where the AGN fraction peaks.
