The SCUBA Half Degree Extragalactic Survey (SHADES) - IX: the environment, mass and redshift dependence of star formation

Abstract

We present a comparison between the SCUBA Half Degree Extragalactic Survey (SHADES) at 450 and 850 microns in the Lockman Hole East with a deep Spitzer Space Telescope survey at 3.6-24 microns conducted in Guaranteed Time. Using stacking analyses we demonstrate a striking correspondence between the galaxies contributing the submm extragalactic background light, with those likely to dominate the backgrounds at Spitzer wavelengths. Using a combination BRIzK plus Spitzer photometric redshifts, we show that at least a third of the Spitzer-identified submm galaxies at 1<z<1.5 appear to reside in overdensities when the density field is smoothed at 0.5-2 Mpc comoving diameters, supporting the high-redshift reversal of the local star formation - galaxy density relation. We derive the dust-shrouded cosmic star formation history of galaxies as a function of assembled stellar masses. For model stellar masses <10^11 Msun, this peaks at lower redshifts than the ostensible z~2.2 maximum for submm point sources, adding to the growing consensus for ``downsizing'' in star formation. Our surveys are also consistent with ``downsizing'' in mass assembly. Both the mean star formation rates <dM/dt> and specific star formation rates <(1/M)dM/dt> are in striking disagreement with some semi-analytic predictions from the Millenium simulation. The discrepancy could either be resolved with a top-heavy initial mass function, or a significant component of the submm flux heated by the interstellar radiation field.

Accepted by MNRAS. SMG environments analysis extended. 17 pages, 18 figures. Includes BoxedEPS

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• A Highly Consistent Framework for the Evolution of the Star-Forming "Main Sequence" from z~0-6
• The star-formation history of K-selected galaxies
• Herschel-ATLAS/GAMA: a census of dust in optically selected galaxies from stacking at submillimetre wavelengths
• The SCUBA-2 Cosmology Legacy Survey: The EGS deep field I - Deep number counts and the redshift distribution of the recovered Cosmic Infrared Background at 450 and 850 um
• The SCUBA Half-Degree Extragalactic Survey (SHADES) - VIII. The Nature of Faint Submm Galaxies in SHADES, SWIRE and SXDF Surveys
• Ultradeep Near-Infrared Observations of GOODS 850-5
• Ultra deep AKARI observations of Abell 2218: resolving the 15 um extragalactic background light