HELP: star formation as function of galaxy environmentwith Herschel

TL;DR

This study uses Herschel data to investigate how the relation between star formation and stellar mass in galaxies depends on environment across redshifts 0.1 to 3.2, revealing environment influences at certain epochs.

Contribution

It provides new insights into the environmental dependence of the star formation main-sequence over a broad redshift range using extensive Herschel data.

Findings

The main-sequence depends on environment at 1.5 < z < 2.

Star formation rate density peaks higher at z ~ 1.9.

Environment influences star formation in specific redshift intervals.

Abstract

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 $z \sim 1.9$.