An ALMA survey of the SCUBA-2 Cosmology Legacy Survey UKIDSS/UDS field: number counts of submillimeter galaxies

S. M. Stach, I. Smail, A. M. Swinbank, J. E. Geach, F. X. An, O. Almaini, V. Arumugam, A. W. Blain, S. C. Chapman, C. J. Conselice, E. A. Cooke, K. E. K. Coppin, J. S. Dunlop, D. Farrah, B. Gullberg, W. Hartley, R. J. Ivison, D. T. Maltby, M. J. Michałowski, D. ScottJ. L. Wardlow, P. van der Werf

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Abstract

We report the first results of AS2UDS, an 870 μm continuum survey with the Atacama Large Millimeter/Submillimeter Array (ALMA) of a total area of ∼50 arcmin 2 comprising a complete sample of 716 submillimeter sources drawn from the SCUBA-2 Cosmology Legacy Survey (S2CLS) map of the UKIDSS/UDS field. The S2CLS parent sample covers a 0.96 degree 2 field at σ 850 = 0.90 ± 0.05 mJy beam -1. Our deep, high-resolution ALMA observations with σ 870 ∼ 0.25 mJy and a 0.″15-0.″30 FWHM synthesized beam, provide precise locations for 695 submillimeter galaxies (SMGs) responsible for the submillimeter emission corresponding to 606 sources in the low-resolution, single-dish map. We measure the number counts of SMGs brighter than S 870 ≥ 4 mJy, free from the effects of blending and show that the normalization of the counts falls by 28% ± 2% in comparison with the SCUBA-2 published counts, but that the shape remains unchanged. We determine that % of the brighter single-dish sources with S 850 ≥ 9 mJy consist of a blend of two or more ALMA-detectable SMGs brighter than S 870 ∼ 1 mJy (corresponding to a galaxy with a total-infrared luminosity of L IR 10 12 L o), in comparison with 28% ± 2% for the single-dish sources at S 850 ≥ 5 mJy. Using the 46 single-dish submillimeter sources that contain two or more ALMA-detected SMGs with photometric redshifts, we show that there is a significant statistical excess of pairs of SMGs with similar redshifts (<1% probability of occurring by chance), suggesting that at least 30% of these blends arise from physically associated pairs of SMGs.

Original languageEnglish
Article number161
JournalThe Astrophysical Journal
Volume860
Issue number2
DOIs
Publication statusPublished - 25 Jun 2018

Keywords

  • galaxies: high-redshift
  • galaxies: starburst

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