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

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 mu 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 CommonUser Bolometer Array 2 (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 HerschelSpectral and Photometric Imaging Receiver (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(-1.66)(+1.35) and 45.80(-3.48)(+2.88) K, a cold-to-hot dust mass ratio of 26.62(-6.74)(+5.61) and a beta of 1.83(-0.28)(+0.14) . 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 mu 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.