The [OIII] emission line luminosity function of optically selected
  type-2 AGN from zCOSMOS
  We present a catalog of 213 type-2 AGN selected from the zCOSMOS survey. The
selected sample covers a wide redshift range (0.15<z<0.92) and is deeper than
any other previous study, encompassing the luminosity range 10^{5.5} < Lsun<
L[OIII] < 10^{9.1} Lsun. We explore the intrinsic properties of these AGN and
the relation to their X-ray emission (derived from the XMM-COSMOS
observations). We study their evolution by computing the [OIII]5007A line
luminosity function (LF) and we constrain the fraction of obscured AGN as a
function of luminosity and redshift. The sample was selected on the basis of
the optical emission line ratios, after applying a cut to the signal-to-noise
ratio (S/N) of the relevant lines. We used the standard diagnostic diagrams
[OIII]/Hbeta versus [NII]/Halpha and ([OIII]/Hbeta versus [SII]/Halpha) to
isolate AGN in the redshift range 0.15<z<0.45 and the diagnostic diagram
[OIII]/Hbeta versus [OII]/Hbeta to extend the selection to higher redshift
(0.5<z<0.92). Combining our sample with one drawn from SDSS, we found that the
best description of the evolution of type-2 AGN is a luminosity-dependent
density evolution model. Moreover, using the type-1 AGN LF we were able to
constrain the fraction of type-2 AGN to the total (type-1 + type-2) AGN
population. We found that the type-2 fraction decreases with luminosity, in
agreement with the most recent results, and shows signs of a slight increase
with redshift. However, the trend with luminosity is visible only after
combining the SDSS+zCOSMOS samples. From the COSMOS data points alone, the
type-2 fraction seems to be quite constant with luminosity.
