Obscured star-formation and environment in the COSMOS field
  We investigate the effects of the environment on star-formation in a sample
of massive luminous and ultra-luminous infrared galaxies (LIRGs and ULIRGs)
with S(24 micron)>80 uJy and i+<24 in the COSMOS field. We exploit the accurate
photometric redshifts in COSMOS to characterize the galaxy environment and
study the evolution of the fraction of LIRGs and ULIRGs in different
environments in the redshift range z=0.3-1.2 and in bins of stellar mass. We
find that the environment plays a role in the star formation processes and
evolution of LIRGs and ULIRGs. We find an overall increase of the ULIRG+LIRG
fraction in an optically-selected sample with increasing redshift, as expected
from the evolution of the star formation rate density. We find that the
ULIRG+LIRG fraction decreases with increasing density up to z~1, and that the
dependence on density flattens with increasing redshift. We do not observe the
reversal of the star-formation rate density relation up to z=1 in massive LIRGs
and ULIRGs, suggesting that such reversal might occur at higher redshift in
this infrared luminosity range.
