HELP: star formation as function of galaxy environmentwith Herschel
  The Herschel Extragalactic Legacy Project (HELP) brings together a vast range
of data from many astronomical observatories. Its main focus is on the Herschel
data, which maps dust obscured star formation over 1300 deg$^2$. With this
unprecedented combination of data sets, it is possible to investigate how the
star formation vs stellar mass relation (main-sequence) of star-forming
galaxies depends on environment. In this pilot study we explore this question
between 0.1 < z < 3.2 using data in the COSMOS field. We estimate the local
environment from a smoothed galaxy density field using the full photometric
redshift probability distribution. We estimate star formation rates by stacking
the SPIRE data from the Herschel Multi-tiered Extragalactic Survey (HerMES).
Our analysis rules out the hypothesis that the main-sequence for star-forming
systems is independent of environment at 1.5 < z < 2, while a simple model in
which the mean specific star formation rate declines with increasing
environmental density gives a better description. However, we cannot exclude a
simple hypothesis in which the main-sequence for star-forming systems is
independent of environment at z < 1.5 and z > 2. We also estimate the evolution
of the star formation rate density in the COSMOS field and our results are
consistent with previous measurements at z < 1.5 and z > 2 but we find a
$1.4^{+0.3}_{-0.2}$ times higher peak value of the star formation rate density
at $z \sim 1.9$.
