The Host-Galaxy Properties of Type 1 Versus Type 2 Active Galactic
  Nuclei
  The unified model of active galactic nuclei (AGNs) proposes that different
AGN optical spectral types are caused by different viewing angles with respect
to an obscuring 'torus'. Therefore, this model predicts that type 1 and type 2
AGNs should have similar host-galaxy properties. We investigate this prediction
with 2463 X-ray selected AGNs in the COSMOS field. We divide our sample into
type 1 and type 2 AGNs based on their spectra, morphologies, and variability.
We derive their host-galaxy stellar masses ($M_\star$) through SED fitting, and
find that the host $M_\star$ of type 1 AGNs tend to be slightly smaller than
those of type 2 AGNs by
$\Delta\overline{\mathrm{log}M_\star}\approx0.2~\mathrm{dex}$ ($\approx
4\sigma$ significance). Besides deriving star-formation rates (SFRs) from SED
fitting, we also utilize far-infrared (FIR) photometry and a stacking method to
obtain FIR-based SFRs. We find that the SFRs of type 1 and type 2 sources are
similar once their redshifts and X-ray luminosities are controlled. We also
investigate cosmic environment, and find that the surface number densities
(sub-Mpc) and cosmic-web environments ($\approx 1\text{--}10$~Mpc) are similar
for both populations. In summary, our analyses show that the host galaxies of
type 1 and type 2 AGNs have similar SFR and cosmic environment in general, but
the former tend to have lower $M_\star$ than the latter. The difference in
$M_\star$ indicates that the AGN unification model is not strictly correct and
both host galaxy and torus may contribute to the optical obscuration of AGNs.
