The Dark Matter Halos of Moderate Luminosity X-ray AGN as Determined
  from Weak Gravitational Lensing and Host Stellar Masses
  Understanding the relationship between galaxies hosting active galactic
nuclei (AGN) and the dark matter halos in which they reside is key to
constraining how black-hole fueling is triggered and regulated. Previous
efforts have relied on simple halo mass estimates inferred from clustering,
weak gravitational lensing, or halo occupation distribution modeling. In
practice, these approaches remain uncertain because AGN, no matter how they are
identified, potentially live a wide range of halo masses with an occupation
function whose general shape and normalization are poorly known. In this work,
we show that better constraints can be achieved through a rigorous comparison
of the clustering, lensing, and cross-correlation signals of AGN hosts to a
fiducial stellar-to-halo mass relation (SHMR) derived for all galaxies. Our
technique exploits the fact that the global SHMR can be measured with much
higher accuracy than any statistic derived from AGN samples alone. Using 382
moderate luminosity X-ray AGN at z<1 from the COSMOS field, we report the first
measurements of weak gravitational lensing from an X-ray selected sample.
Comparing this signal to predictions from the global SHMR, we find that,
contrary to previous results, most X-ray AGN do not live in medium size groups
---nearly half reside in relatively low mass halos with Mh~10^12.5 Msun. The
AGN occupation function is well described by the same form derived for all
galaxies but with a lower normalization---the fraction of halos with AGN in our
sample is a few percent. By highlighting the relatively "normal" way in which
moderate luminosity X-ray AGN hosts occupy halos, our results suggest that the
environmental signature of distinct fueling modes for luminous QSOs compared to
moderate luminosity X-ray AGN is less obvious than previously claimed.
