Upon its completion the Herschel ATLAS (H-ATLAS) will be the largest submillimetre survey to date, detecting close to half-a-million sources. It will only be possible to measure spectroscopic redshifts for a small fraction of these sources. However, if the rest-frame spectral energy distribution (SED) of a typical H-ATLAS source is known, this SED and the observed Herschel fluxes can be used to estimate the redshifts of the H-ATLAS sources without spectroscopic redshifts. In this paper, we use a subset of 40 H-ATLAS sources with previously measured redshifts in the range 0.5 < z < 4.2 to derive a suitable average template for high redshift H-ATLAS sources. We find that a template with two dust components (T c = 23.9 K, T h = 46.9 K and ratio of mass of cold dust to mass of warm dust of 30.1) provides a good fit to the rest-frame fluxes of the sources in our calibration sample. We use a jackknife technique to estimate the accuracy of the redshifts estimated with this template, finding a root mean square of ∆z/(1 + z) = 0.26. For sources for which there is prior information that they lie at z > 1 we estimate that the rms of ∆z/(1 + z) = 0.12. We have used this template to estimate the redshift distribution for the sources detected in the H-ATLAS equatorial fields, finding a bimodal distribution with a mean redshift of 1.2, 1.9 and 2.5 for 250, 350 and 500 µm selected sources respectively.
We investigate the multi-wavelength properties of a sample of 450-µm selected sources from the SCUBA-2 Cosmology Legacy Survey (S2CLS). A total of 69 sources were identified above 4σ in deep SCUBA-2 450-µm observations overlapping the UDS and COSMOS fields and covering 210 arcmin 2 to a typical depth of σ 450 = 1.5 mJy. Reliable cross identification are found for 58 sources (84 per cent) in Spitzer and Hubble Space Telescope WFC3/IR data. The photometric redshift distribution (dN/dz) of 450 µm-selected sources is presented, showing a broad peak in the redshift range 1 < z < 3, and a median of z = 1.4. Combining the SCUBA-2 photometry with Herschel SPIRE data from HerMES, the submm spectral energy distribution (SED) is examined via the use of modified blackbody fits, yielding aggregate values for the IR luminosity, dust temperature and emissivity of L IR = 10 12±0.8 L ⊙ , T D = 42 ± 11 K and β D = 1.6 ± 0.5, respectively. The relationship between these SED parameters and the physical properties of galaxies is investigated, revealing correlations between T D and L IR and between β D and both stellar mass and effective radius. The connection between star formation rate and stellar mass is explored, with 24 per cent of 450 µm sources found to be "star-bursts", i.e. displaying anomalously high specific SFRs. However, both the number density and observed properties of these "star-burst" galaxies are found consistent with the population of normal star-forming galaxies. c 2013 RAS 2 I.G. Roseboom et al.
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