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

Bakx, Tom J. L. C.; Eales, S. A.; Negrello, M.; Smith, M. W. L.; Valiante, E.; Holland, W. S.; Baes, M.; Bourne, N.; Clements, D. L.; Dannerbauer, H.; De Zotti, G.; Dunne, L.; Dye, S.; Furlanetto, C.; Ivison, R. J.; Maddox, S.; Marchetti, L.; Michałowski, M. J.; Omont, A.; Oteo, I.; Wardlow, J. L.; van der Werf, P. and Yang, C. (2018). The Herschel Bright Sources (HerBS): sample definition and SCUBA-2 observations. Monthly Notices of the Royal Astronomical Society, 473(2) pp. 1751–1773.

DOI: https://doi.org/10.1093/mnras/stx2267

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 µm 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 µm of 189 galaxies of the HerBS sample, 152 of these sources
were detected. We fit a spectral template to the Herschel-SPIRE and 850 µm 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 K and 45.80+2.88 −3.48 K, a cold-to-hot dust mass ratio of 26.62+5.61 −6.74 and a β 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 is high. Out of the 152 SCUBA-2 detected galaxies, the model predicts 128.4 ± 2.1 of those galaxies to be lensed (84.5%). The SPIRE 500 µm 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.

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