Differences in Halo-Scale Environments between Type 1 and Type 2 AGNs at
  Low Redshift
  Using low-redshift (z<0.09) samples of AGNs, normal galaxies and groups of
galaxies selected from the Sloan Digital Sky Survey (SDSS), we study the
environments of type 1 and type 2 AGNs both on small and large scales.
Comparisons are made for galaxy samples matched in redshift, $r$-band
luminosity, [OIII] luminosity, and also the position in groups (central or
satellite). We find that type 2 AGNs and normal galaxies reside in similar
environments. Type 1 and type 2 AGNs have similar clustering properties on
large scales ($\gtrsim1$Mpc), but at scales smaller than 100 kpc, type 2s have
significant more neighbors than type 1s ($3.09\pm0.69$ times more for central
AGNs at $\lesssim30$kpc). These results suggest that type 1 and type 2 AGNs are
hosted by halos of similar masses, as is also seen directly from the mass
distributions of their host groups ($\sim10^{12}h^{-1} M_{\odot}$ for centrals
and $\sim10^{13}h^{-1} M_{\odot}$ for satellites). Type~2s have significantly
more satellites around them, and the distribution of their satellites is also
more centrally concentrated. The host galaxies of both types of AGNs have
similar optical properties, but their infrared colors are significantly
different. Our results suggest that the simple unified model based solely on
torus orientation is not sufficient, but that galaxy interactions in dark
matter halos must have played an important role in the formation of the dust
structure that obscures AGNs.
