Investigating the relationship between AGN activity and stellar mass in
  zCOSMOS galaxies at 0<z<1 using emission line diagnostic diagrams
  We investigate the link between AGN activity, star-formation and stellar mass
of the host galaxy at 0<z<1, looking for spectroscopic traces of AGN and aging
of the host. This work provides an extension of the existing studies at z<0.1
and contributes to shed light on galaxy evolution at intermediate redshifts. We
used the zCOSMOS 20k data to create a sample of galaxies at z<1. We divided the
sample in several mass-redshift bins to obtain stacked galaxy spectra with an
improved S/N. We exploited emission-line diagnostic diagrams to separate AGN
from star-forming galaxies. We found indication of a role for the total galaxy
stellar mass in leading galaxy classification. Stacked spectra show AGN
signatures above the log M_*/M_sun>10.2 threshold. Moreover, the stellar
populations of AGN hosts are found to be older with respect to star-forming and
composites galaxies. This could be due to the the tendency of AGN to reside in
massive hosts. The dependence of the AGN classification on the stellar mass is
in agreement with what has been already found in previous studies. It is
consistent with, together with the evidence of older stellar populations
inhabiting the AGN-like galaxies, the downsizing scenario. In particular, our
evidence points to an evolutionary scenario where the AGN-feedback is capable
of quenching the star formation in the most massive galaxies. Therefore, the
AGN-feedback is the best candidate for initiating the passive evolutionary
phase of galaxies.
