ALMA observations of cold molecular gas in AGN hosts at z~1.5 - Evidence
  of AGN feedback?
  Similarly to the cosmic star formation history, the black hole accretion rate
density of the Universe peaked at 1<z<3. This cosmic epoch is hence best suited
for investigating the effects of radiative feedback from AGN. Observational
efforts are underway to quantify the impact of AGN feedback, if any, on their
host galaxies. Here we present a study of the molecular gas content of AGN
hosts at z~1.5 using CO[2-1] line emission observed with ALMA for a sample of
10 AGNs. We compare this with a sample of galaxies without an AGN matched in
redshift, stellar mass, and star formation rate. We detect CO in 3 AGNs with
$\mathrm{L_{CO} \sim 6.3-25.1\times 10^{9} L_{\odot}}$ which translates to a
molecular hydrogen gas mass of $\mathrm{2.5-10\times 10^{10} M_{\odot}}$
assuming conventional conversion factor of $\mathrm{\alpha_{CO}}\sim3.6$. Our
results indicate a >99% probability of lower depletion time scales and lower
molecular gas fractions in AGN hosts with respect to the non-AGN comparison
sample. We discuss the implications of these observations on the impact that
AGN feedback may have on star formation efficiency of z>1 galaxies.
