The SCUBA-2 Cosmology Legacy Survey: ALMA resolves the bright-end of the submillimeter number counts

Simpson, J.M.; Smail, I.; Swinbank, A.M.; Chapman, S.C.; Geach, J.E.; Ivison, R.J.; Thomson, A.P.; Aretxaga, I.; Blain, A.W.; Cowley, W.I.; Chen, C.-C.; Coppin, K.E.K.; Dunlop, J.S.; Edge, A.C.; Farrah, D.; Ibar, E.; Karim, A.; Knudsen, K.K.; Meijerink, R.; Michałowski, M.J.; Scott, D.; Spanns, M.; van der Werf, P.P.

Abstract

We present high-resolution 870 μm Atacama Large Millimeter/sub-millimeter Array (ALMA) continuum maps of 30 bright sub-millimeter sources in the UKIDSS UDS field. These sources are selected from deep, 1 degree2 850 μm maps from the SCUBA-2 Cosmology Legacy Survey, and are representative of the brightest sources in the field (median = 8.7 ± 0.4 mJy). We detect 52 sub-millimeter galaxies (SMGs) at >4σ significance in our 30 ALMA maps. In of the ALMA maps the single-dish source comprises a blend of ≥2 SMGs, where the secondary SMGs are Ultra-luminous Infrared Galaxies (ULIRGs) with 1012 . The brightest SMG contributes on average of the single-dish flux density, and in the ALMA maps containing ≥2 SMGs the secondary SMG contributes of the integrated ALMA flux. We construct source counts and show that multiplicity boosts the apparent single-dish cumulative counts by 20% at S870 > 7.5 mJy, and by 60% at S870 > 12 mJy. We combine our sample with previous ALMA studies of fainter SMGs and show that the counts are well-described by a double power law with a break at 8.5 ± 0.6 mJy. The break corresponds to a luminosity of ~6 × 1012 or a star formation rate (SFR) of ~103 . For the typical sizes of these SMGs, which are resolved in our ALMA data with = 1.2 ± 0.1 kpc, this yields a limiting SFR density of ~100 yr−1 kpc−2 Finally, the number density of S870 2 mJy SMGs is 80 ± 30 times higher than that derived from blank-field counts. An over-abundance of faint SMGs is inconsistent with line-of-sight projections dominating multiplicity in the brightest SMGs, and indicates that a significant proportion of these high-redshift ULIRGs are likely to be physically associated.

Citation

Simpson, J., Smail, I., Swinbank, A., Chapman, S., Geach, J., Ivison, R., …van der Werf, P. (2015). The SCUBA-2 Cosmology Legacy Survey: ALMA resolves the bright-end of the submillimeter number counts. Astrophysical Journal, 807(2), Article 128. https://doi.org/10.1088/0004-637x/807/2/128

• Journal Article Type: Article
• Acceptance Date: May 18, 2015
• Publication Date: Jul 10, 2015
• Deposit Date: Jul 14, 2015
• Publicly Available Date: Jul 23, 2015
• Journal: Astrophysical Journal
• Print ISSN: 0004-637X
• Electronic ISSN: 1538-4357
• Publisher: American Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 807
• Issue: 2
• Article Number: 128
• DOI: https://doi.org/10.1088/0004-637x/807/2/128
• Keywords: Galaxies: abundances, Galaxies: high-redshift, Galaxies: starburst, Galaxies: star formation, Submillimeter: galaxies.