The GALEX view of the Herschel Reference Survey - Ultraviolet structural
  properties of nearby galaxies
  We present GALEX far-ultraviolet (FUV) and near-ultraviolet (NUV) as well as
SDSS g, r, i photometry and structural parameters for the Herschel Reference
Survey, a magnitude-, volume-limited sample of nearby galaxies in different
environments. We use this unique dataset to investigate the ultraviolet (UV)
structural scaling relations of nearby galaxies and to determine how the
properties of the UV disk vary with atomic hydrogen content and environment. We
find a clear change of slope in the stellar mass vs. effective surface
brightness relation when moving from the optical to the UV, with more massive
galaxies having brighter optical but fainter UV surface brightnesses than
smaller systems. A similar change of slope is also seen in the radius vs.
surface brightness relation. By comparing our observations with the predictions
of a simple multi-zone chemical model of galaxy evolution, we show that these
findings are a natural consequence of a much more efficient inside-out growth
of the stellar disk in massive galaxies. We confirm that isophotal radii are
always a better proxy for the size of the stellar/star-forming disk than
effective quantities and we show that the extent of the UV disk (normalized to
the optical size) is strongly correlated to the integrated HI gas fraction.
This relation still holds even when cluster spirals are considered, with
HI-deficient systems having less extended star-forming disks than HI-normal
galaxies. Interestingly, the star formation in the inner part of HI-deficient
galaxies is significantly less affected by the removal of the atomic hydrogen,
as expected in a simple ram-pressure stripping scenario. These results suggest
that it is the amount of HI that regulates the growth of the star-forming disk
in the outskirts of galaxies.
