ALFALFA HI Data Stacking II. HI content of the host galaxies of AGN
  We use a stacking technique to measure the average HI content of a
volume-limited sample of 1871 AGN host galaxies from a parent sample of
galaxies selected from the SDSS and GALEX imaging surveys with stellar masses
greater than 10^10 M_sun and redshifts in the range 0.025<z<0.05. HI data are
available from the Arecibo Legacy Fast ALFA (ALFALFA) survey. In previous work,
we found that the HI gas fraction in galaxies correlates most strongly with the
combination of optical/UV colour and stellar surface mass density. We therefore
build a control sample of non-AGN matched to the AGN hosts in these two
properties. We study trends in HI gas mass fraction (M(HI)/M_*), where M_* is
the stellar mass) as a function of black hole accretion rate indicator
L[OIII]/M(BH). We find no significant difference in HI content between AGN and
control samples at all values of black hole accretion rate probed by the
galaxies in our sample. This indicates that AGN do not influence the
large-scale gaseous properties of galaxies in the local Universe. We have
studied the variation in HI mass fraction with black hole accretion rate in the
blue and red galaxy populations. In the blue population, the HI gas fraction is
independent of accretion rate, indicating that accretion is not sensitive to
the properties of the interstellar medium of the galaxy on large scales.
However, in the red population accretion rate and gas fraction do correlate.
The measured gas fractions in this population are not too different from the
ones expected from a stellar mass loss origin, implying that the fuel supply in
the red AGN population could be a mixture of mass loss from stars and gas
present in disks.
