Arecibo Legacy Fast ALFA H i data stacking - II. H i content of the host galaxies of active galactic nuclei

Abstract

We use a stacking technique to measure the average H I content of a volume-limited sample of 1871 active galactic nucleus (AGN) host galaxies from a parent sample of galaxies selected from the Sloan Digital Sky Survey and GALEX imaging surveys with stellar masses greater than 10 10 Mand redshifts in the range 0.025 < z < 0.05. H I data are available from the Arecibo Legacy Fast ALFA (ALFALFA) survey. In previous work, we found that the H I gas fraction in galaxies correlates most strongly with the combination of optical/ultraviolet 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 H I gas mass fraction (MH I/M� , where Mis the stellar mass) as a function of black hole accretion rate indicator L(O III)/MBH. We find no significant difference in H I 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 H I mass fraction with black hole accretion rate in the blue and red galaxy populations. In the blue population, the H I 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 discs.