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arXiv · 1805.05362

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. M. Simpson·J. E. Geach·F. X. An·O. Almaini·V. Arumugam·A. W. Blain·S. C. Chapman·C. -C. Chen·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. Scott·C. Simpson·A. P. Thomson·J. L. Wardlow·P. van der Werf
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Abstract

We report the first results of AS2UDS: an 870 $\mu$m continuum survey with the Atacama Large Millimeter/Submillimeter Array (ALMA) of a total area of $\sim$ 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 $\sigma_{850}=0.90\pm0.05$ mJy beam$^{-1}$. Our deep, high-resolution ALMA observations with $\sigma_{\rm 870}\sim$ 0.25 mJy and a 0.15"--0.30" FWHM synthesized beam, provide precise locations for 695 submillimetre 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 $S_{\rm 870}\geq$ 4 mJy, free from the effects of blending and show that the normalisation of the counts falls by 28 $\pm$ 2% in comparison to the SCUBA-2 parent sample, but that the shape remains unchanged. We determine that 44$^{+16}_{-14}$% of the brighter single-dish sources with $S_{850}\geq$ 9 mJy consist of a blend of two or more ALMA-detectable SMGs brighter than $S_{870}\sim$ 1 mJy (corresponding to a galaxy with a total-infrared luminosity of $L_{IR}\geq$ 10$^{12}$ L$_\odot$), in comparison to 28 $\pm$ 2% for the single-dish sources at $S_{\rm 850}\geq$ 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.

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S. M. Stach, I. Smail, A. M. Swinbank, J. M. Simpson, J. E. Geach, F. X. An, O. Almaini, V. Arumugam, A. W. Blain, S. C. Chapman, C. -C. Chen, 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. Scott, C. Simpson, A. P. Thomson, J. L. Wardlow, P. van der Werf. 2018-05-14. An ALMA survey of the SCUBA-2 Cosmology Legacy Survey UKIDSS/UDS field: number counts of submillimeter galaxies. https://doi.org/10.3847/1538-4357/aac5e5

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