Measures of star formation rates from Infrared (Herschel) and UV (GALEX)
  emissions of galaxies in the HerMES fields
  The reliability of infrared (IR) and ultraviolet (UV) emissions to measure
star formation rates in galaxies is investigated for a large sample of galaxies
observed with the SPIRE and PACS instruments on Herschel as part of the HerMES
project. We build flux-limited 250 micron samples of sources at redshift z<1,
cross-matched with the Spitzer/MIPS and GALEX catalogues. About 60 % of the
Herschel sources are detected in UV. The total IR luminosities, L_IR, of the
sources are estimated using a SED-fitting code that fits to fluxes between 24
and 500 micron. Dust attenuation is discussed on the basis of commonly-used
diagnostics: the L_IR/L_UV ratio and the slope, beta, of the UV continuum. A
mean dust attenuation A_UV of ~ 3 mag is measured in the samples. L_IR/L_UV is
found to correlate with L_IR. Galaxies with L_IR > 10 ^{11} L_sun and 0.5< z<1
exhibit a mean dust attenuation A_UV about 0.7 mag lower than that found for
their local counterparts, although with a large dispersion. Our galaxy samples
span a large range of beta and L_IR/L_UV values which, for the most part, are
distributed between the ranges defined by the relations found locally for
starburst and normal star-forming galaxies. As a consequence the recipe
commonly applied to local starbursts is found to overestimate the dust
attenuation correction in our galaxy sample by a factor ~2-3 .
