The SAURON project - XIII. SAURON-GALEX study of early-type galaxies:
  the ultraviolet colour-magnitude relations and Fundamental Planes
  We present GALEX far (FUV) and near (NUV) ultraviolet imaging of 34 nearby
early-type galaxies from the SAURON representative sample of 48 E/S0 galaxies,
all of which have ground-based optical imaging from the MDM Observatory. The
surface brightness profiles of nine galaxies show regions with blue UV-optical
colours suggesting recent star formation. Five of these show blue integrated
UV-optical colours that set them aside in the NUV integrated colour-magnitude
relation. They also have other properties confirming they have had recent star
formation, in particular H_beta absorption higher than expected for a quiescent
population and a higher CO detection rate. NUV-blue galaxies are generally
drawn from the lower stellar velocity dispersion and thus lower dynamical mass
part of the sample. We have also constructed the first UV Fundamental Planes
and show that NUV blue galaxies bias the slopes and increase the scatters. If
they are eliminated the fits get closer to expectations from the virial
theorem. Although our analysis is based on a limited sample, it seems that a
dominant fraction of the tilt and scatter of the UV Fundamental Planes is due
to the presence of young stars in preferentially low-mass early-type galaxies.
Interestingly, the UV-optical radial colour profiles reveal a variety of
behaviours, with many galaxies showing signs of recent star formation, a
central UV-upturn phenomenon, smooth but large-scale age and metallicity
gradients, and in many cases a combination of these. In addition, FUV-NUV and
FUV-V colours even bluer than those normally associated with UV-upturn galaxies
are observed at the centre of some quiescent galaxies. Four out of the five
UV-upturn galaxies are slow rotators. These objects should thus pose
interesting challenges to stellar evolutionary models of the UV-upturn.
