The Herschel Bright Sources (HerBS): Sample definition and SCUBA-2 observations

TL;DR

This paper introduces the HerBS sample of high-redshift Herschel sources, presents SCUBA-2 observations, and analyzes their dust properties and lensing fractions, revealing a high prevalence of gravitational lensing among these bright, distant galaxies.

Contribution

The study provides the first detailed analysis of the Herschel Bright Sources sample, including SCUBA-2 observations and dust temperature estimates, highlighting the high lensing fraction in this population.

Findings

152 of 189 observed sources detected with SCUBA-2

Dust temperatures of approximately 21 K and 46 K derived from spectral fitting

Estimated 76% of the sources are gravitationally lensed

Abstract

We present the Herschel Bright Sources (HerBS) sample, a sample of bright, high-redshift Herschel sources detected in the 616.4 square degree H-ATLAS survey. The HerBS sample contains 209 galaxies, selected with a 500 {\mu}m flux density greater than 80 mJy and an estimated redshift greater than 2. The sample consists of a combination of HyLIRGs and lensed ULIRGs during the epoch of peak cosmic star formation. In this paper, we present SCUBA-2 observations at 850 ${\mu}$m of 189 galaxies of the HerBS sample, 152 of these sources were detected. We fit a spectral template to the Herschel-SPIRE and 850 ${\mu}$m SCUBA-2 flux densities of 22 sources with spectroscopically determined redshifts, using a two-component modified blackbody spectrum as a template. We find a cold- and hot-dust temperature of 21.29 K and 45.80 K, a cold-to-hot dust mass ratio of 26.62 and a $\beta$ of 1.83. The poor quality of the fit suggests that the sample of galaxies is too diverse to be explained by our simple model. Comparison of our sample to a galaxy evolution model indicates that the fraction of lenses is high. Out of the 152 SCUBA-2 detected galaxies, the model predicts 128.4 $\pm$ 2.1 of those galaxies to be lensed (84.5%). The SPIRE 500 ${\mu}$m flux suggests that out of all 209 HerBS sources, we expect 158.1 $\pm$ 1.7 lensed sources, giving a total lensing fraction of 76 per cent.