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

TL;DR

This study compares submillimeter and infrared galaxy surveys to explore the environment, mass, and redshift dependence of star formation, revealing evidence for downsizing and discrepancies with theoretical models.

Contribution

It provides new insights into the cosmic star formation history and galaxy mass assembly, highlighting the role of environment and challenging existing semi-analytic predictions.

Findings

At least a third of submm galaxies at 1<z<1.5 are in overdensities.

Star formation peaks at lower redshifts for less massive galaxies, supporting downsizing.

Observed star formation rates disagree with some semi-analytic models.

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.