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

Abstract

We present the Herschel Bright Sources (HerBS) sample, a sample of bright, high-redshift Herschel sources detected in the 616.4 deg 2 Herschel Astrophysical Terahertz Large Area Survey. The HerBS sample contains 209 galaxies, selected with a 500 m flux density greater than 80 mJy and an estimated redshift greater than 2. The sample consists of a combination of hyperluminous infrared galaxies and lensed ultraluminous infrared galaxies during the epoch of peak cosmic star formation. In this paper, we present Submillimetre Common-User Bolometer Array 2 (SCUBA-2) observations at 850 m of 189 galaxies of the HerBS sample, 152 of these sources were detected. We fit a spectral template to the Herschel-Spectral and Photometric Imaging Receiver (SPIRE) and 850 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 +1.35 -1.66 and 45.80 +2.88 -3.48 K, a cold-to-hot dust mass ratio of 26.62 +5.61 -6.74 and a of 1.83 +0.14 -0.28 . 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 are high. Out of the 152 SCUBA-2 detected galaxies, the model predicts 128.4 2.1 of those galaxies to be lensed (84.5 per cent). The SPIRE 500 m flux suggests that out of all 209 HerBS sources, we expect 158.1 1.7 lensed sources, giving a total lensing fraction of 76 per cent.