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An ALMA survey of the brightest sub-millimetre sources in the SCUBA-2–COSMOS field.

Simpson, J.M. and Smail, I. and Dudzevičiūtė, U. and Matsuda, Y. and Hsieh, B-C. and Wang, W-H. and Swinbank, A.M. and Stach, S.M. and An, Fang Xia and Birkin, J.E. and Ao, Y. and Bunker, A.J. and Chapman, S.C. and Chen, Chian-Chou and Coppin, K.E.K. and Ikarashi, S. and Ivison, R.J. and Mitsuhashi, I. and Saito, T. and Umehata, H. and Wang, R. and Zhao, Y. (2020) 'An ALMA survey of the brightest sub-millimetre sources in the SCUBA-2–COSMOS field.', Monthly notices of the Royal Astronomical Society., 495 (3). pp. 3409-3430.


We present an ALMA study of the ∼ 180 brightest sources in the SCUBA-2 850-μm map of the COSMOS field from the S2COSMOS survey, as a pilot study for AS2COSMOS – a full survey of the ∼ 1,000 sources in this field. In this pilot we have obtained 870-μm continuum maps of an essentially complete sample of the brightest 182 sub-millimetre sources (⁠S850μm> 6.2 mJy) in COSMOS. Our ALMA maps detect 260 sub-millimetre galaxies (SMGs) spanning a range in flux density of S870μm = 0.7–19.2 mJy. We detect more than one SMG counterpart in 34 ± 2 per cent of sub-millimetre sources, increasing to 53 ± 8 per cent for SCUBA-2 sources brighter than S850μm> 12 mJy. We estimate that approximately one-third of these SMG–SMG pairs are physically associated (with a higher rate for the brighter secondary SMGs, S870μm≳ 3 mJy), and illustrate this with the serendipitous detection of bright [C II] 157.74 μm line emission in two SMGs, AS2COS 0001.1 & 0001.2 at z = 4.63, associated with the highest significance single-dish source. Using our source catalogue we construct the interferometric 870-μm number counts at S870μm> 6.2 mJy. We use the extensive archival data of this field to construct the multiwavelength spectral energy distribution of each AS2COSMOS SMG, and subsequently model this emission with MAGPHYS to estimate their photometric redshifts. We find a median photometric redshift for the S870μm> 6.2 mJy AS2COSMOS sample of z = 2.87 ± 0.08, and clear evidence for an increase in the median redshift with 870-μm flux density suggesting strong evolution in the bright-end of the 870 μm luminosity function.

Item Type:Article
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Publisher statement:This article has been accepted for publication in Monthly notices of the Royal Astronomical Society. ©: 2020 The Author(s) . Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Date accepted:07 May 2020
Date deposited:19 May 2020
Date of first online publication:18 May 2020
Date first made open access:18 May 2020

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