A complete distribution of redshifts for sub-millimetre galaxies in the SCUBA-2 Cosmology Legacy Survey UDS field

Abstract

Sub-milllimetre galaxies (SMGs) are some of the most luminous star-forming galaxies in the Universe, however their properties remain hard to determine due to the difficulty of identifying their optical\slash near-infrared counterparts. One of the key steps to determining the nature of SMGs is measuring a redshift distribution representative of the whole population. We do this by applying statistical techniques to a sample of 761 850$\mu$m sources from the SCUBA-2 Cosmology Legacy Survey observations of the UKIDSS Ultra-Deep Survey (UDS) Field. We detect excess galaxies around $>98.4$ per cent of the 850$\mu$m positions in the deep UDS catalogue, giving us the first 850$\mu$m selected sample to have virtually complete optical\slash near-infrared redshift information. Under the reasonable assumption that the redshifts of the excess galaxies are representative of the SMGs themselves, we derive a median SMG redshift of $z=2.05\pm 0.03$, with 68 per cent of SMGs residing between $1.07<z<3.06$. We find an average of $1.52\pm 0.09$ excess $K$-band galaxies within 12 arc sec of an 850$\mu$m position, with an average stellar mass of $2.2\pm 0.1\times 10^{10}$ M${}_{\odot }$. While the vast majority of excess galaxies are star-forming, $8.0\pm 2.1$ per cent have passive rest-frame colours, and are therefore unlikely to be detected at sub-millimetre wavelengths even in deep interferometry. We show that brighter SMGs lie at higher redshifts, and use our SMG redshift distribution -- along with the assumption of a universal far-infrared SED -- to estimate that SMGs contribute around 30 per cent of the cosmic star formation rate density between $0.5<z<5.0$.

10 pages, 8 figures, accepted for publication in MNRAS

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• The East Asian Observatory SCUBA--2 survey of the COSMOS field: unveiling 1147 bright sub-millimeter sources across 2.6 square degrees
• Characterization of Two 2mm-detected Optically-Obscured Dusty Star-Forming Galaxies
• Submillimetre galaxies in cosmological hydrodynamical simulations -- an opportunity for constraining feedback models
• Resolving a dusty, star-forming SHiZELS galaxy at z=2.2 with HST, ALMA and SINFONI on kiloparsec scales
• Submillimetre galaxies in two massive protoclusters at z = 2.24: witnessing the enrichment of extreme starbursts in the outskirts of HAE density peaks
• The second Herschel-ATLAS Data Release - III: optical and near-infrared counterparts in the North Galactic Plane field
• Source structure and molecular gas properties from high-resolution CO imaging of SPT-selected dusty star-forming galaxies
• A SCUBA-2 Selected Herschel-SPIRE Dropout and the Nature of this Population
• Modeling submillimeter galaxies in cosmological simulations: Contribution to the cosmic star formation density and predictions for future surveys
• Simultaneously Modelling Dusty Star Forming Galaxies and Massive Quiescents: A Calibration Framework for Galaxy Formation Models