The Lockman Hole project: gas and galaxy properties from a stacking
  experiment
  We perform an HI stacking analysis to study the relation between HI content
and optical/radio/IR properties of galaxies located in the Lockman Hole area.
In the redshift range covered by the observations (up to z = 0.09), we use the
SDSS to separate galaxies with different optical characteristics, and we
exploit the deep L-band radio continuum image (with noise 11 \mu Jy/beam) to
identify galaxies with radio continuum emission. Infrared properties are
extracted from the Spitzer catalog. We detect HI in blue galaxies, but HI is
also detected in the group of red galaxies - albeit with smaller amounts than
for the blue sample. We identify a group of optically inactive galaxies with
early-type morphology that does not reveal any HI and ionized gas. These
inactive galaxies likely represent the genuine red and dead galaxies depleted
of all gas. Unlike inactive galaxies, HI is detected in red LINER-like objects.
Galaxies with radio continuum counterparts mostly belong to the sub-mJy
population, whose objects are thought to be a mixture of star-forming galaxies
and low-power AGNs. After using several AGN diagnostics, we conclude that the
radio emission in the majority of our sub-mJy radio sources stems from star
formation. LINERs appear to separate into two groups based on IR properties and
HI content. LINERs with a 24 \mu m detection show relatively large amounts of
HI and are also often detected in radio continuum as a result of ongoing star
formation. The LINER galaxies which are not detected at 24 \mu m are more like
the optically inactive galaxies by being depleted of HI gas and having no sign
of star formation. Radio LINERs in the latter group are the best candidates for
hosting low-luminosity radio AGN.
