An ALMA Survey of the SCUBA-2 Cosmology Legacy Survey UKIDSS/UDS Field: Number Counts of Submillimeter Galaxies

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, singledish map. We measure the number counts of SMGs brighter than S 870 ≥ 4 mJy, free from the effects of blending and show that the normalisation of the counts falls by 28 ± 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 ≥ 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 totalinfrared luminosity of L IR > ∼ 10 12 L ), in comparison to 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.

A Machine-learning Method for Identifying Multiwavelength Counterparts of Submillimeter Galaxies: Training and Testing Using AS2UDS and ALESS

“…From ALMA follow-up observations of the 716 SCUBA-2-detected submillimeter sources in the S2CLS UKIDSS-UDS field (Stach et al 2018a; S. M. Stach et al 2018b, in preparation), we exploit a sample of 695 SMGs (>4.3σ) within 608 ALMA maps. We label the other 108 ALMA maps that do not contain a >4.3σ ALMA SMG as "blank-ALMA" maps.…”

“…To improve on this situation and so construct more complete samples of SMGs, it is necessary to combine a broader range of multiwavelength properties to isolate potential SMGs from the less active galaxies that are found within the error circles of single-dish submillimeter sources (e.g., Chapin et al 2011;Alberts et al 2013;. One additional complication of these statistical identifications is the fact that recent studies using interferometric observations in the submillimeter/millimeter suggest that 20% of single-dishdetected submillimeter sources actually correspond to blends of multiple SMGs (e.g., Wang et al 2011;Karim et al 2013;Simpson et al 2015aSimpson et al , 2015bStach et al 2018a).…”

An ALMA survey of the SCUBA-2 cosmology legacy survey UKIDSS/UDS field: Dust attenuation in high-redshift Lyman-break galaxies

“…The starting point for our analysis is the catalogue of 716 sub-millimetre sources detected in the 850-µm map of the UDS field from the SCUBA-2 Cosmology Legacy Survey (Geach et al 2017). These were subsequently followed up with ALMA 870 µm (Band-7) imaging between November 2013 and May 2017, with an initial pilot study of 30 of the brightest SCUBA-2 sources in Cycle 1 by Simpson et al (2017), see also Simpson et al (2015b,a), and then subsequent observations to complete the full sample in Cycles 3, 4 and 5 by Stach et al (2019), see also Stach et al (2018). For the completed AS2UDS survey, sources were identified by Stach et al (2019) using cleaned, 0.5 arcsec FWHM-tapered continuum maps, with average depths of σ 870 = 0.25, 0.34, 0.23 and 0.09 mJy beam −1 (Cycles 1, 3, 4 and 5, respectively).…”

An insight into the extragalactic transient and variable microJy radio sky across multiple decades

“…In order to determine the appropriate signal-to-noise (S/N) threshold at which to allow PYBDSF to identify and catalogue sources in our maps, we adopt the empirical 'purity' parameter of Stach et al (2018). We ran PYBDSF on the real and inverted images (i.e.…”