HerMES: Unveiling obscured star formation - the far infrared luminosity
  function of ultraviolet-selected galaxies at z~1.5
  We study the far-infrared (IR) and sub-millimeter properties of a sample of
ultraviolet (UV) selected galaxies at z\sim1.5. Using stacking at 250, 350 and
500 um from Herschel Space Observatory SPIRE imaging of the COSMOS field
obtained within the HerMES key program, we derive the mean IR luminosity as a
function of both UV luminosity and slope of the UV continuum beta. The IR to UV
luminosity ratio is roughly constant over most of the UV luminosity range we
explore. We also find that the IR to UV luminosity ratio is correlated with
beta. We observe a correlation that underestimates the correlation derived from
low-redshift starburst galaxies, but is in good agreement with the correlation
derived from local normal star-forming galaxies. Using these results we
reconstruct the IR luminosity function of our UV-selected sample. This
luminosity function recovers the IR luminosity functions measured from IR
selected samples at the faintest luminosities (Lir ~ 10^{11} L_sun), but might
underestimate them at the bright-end (Lir > 5.10^{11} L_sun). For galaxies with
10^{11}<Lir/L_sun<10^{13}, the IR luminosity function of a UV selection
recovers (given the differences in IR-based estimates) 52-65 to 89-112 per cent
of the star-formation rate density derived from an IR selection. The cosmic
star-formation rate density derived from this IR luminosity function is 61-76
to 100-133 per cent of the density derived from IR selections at the same
epoch. Assuming the latest Herschel results and conservative stacking
measurements, we use a toy model to fully reproduce the far IR luminosity
function from our UV selection at z\sim 1.5. This suggests that a sample around
4 magnitudes deeper (i.e. reaching u \sim 30 mag) and a large dispersion of the
IR to UV luminosity ratio are required.
