THE SCUBA-2 COSMOLOGY LEGACY SURVEY: ALMA RESOLVES THE BRIGHT-END OF THE SUB-MILLIMETER NUMBER COUNTS

• Published in: The Astrophysical journal 2015-07, Vol.807 (2), p.1-13
• Main Authors: Simpson, J. M., Smail, Ian, Swinbank, A. M., Chapman, S. C., Geach, J. E., Ivison, R. J., Thomson, A. P., Aretxaga, I., Blain, A. W., Cowley, W. I., Chen, Chian-Chou, Coppin, K. E. K., Dunlop, J. S., Edge, A. C., Farrah, D., Ibar, E., Karim, A., Knudsen, K. K., Meijerink, R., Micha owski, M. J., Scott, D., Spaans, M., P. P. van der Werf
• Format: Article
• Language: English
• Subjects: ABUNDANCE; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COSMOLOGY; Counting; DENSITY; Flux; FLUX DENSITY; GALAXIES; galaxies: abundances; galaxies: high-redshift; galaxies: star formation; galaxies: starburst; Infrared; LUMINOSITY; MULTIPLICITY; Radio telescopes; RED SHIFT; STAR EVOLUTION; STARS; submillimeter: galaxies
• ISSN: 0004-637X; 1538-4357; 1538-4357
• DOI: 10.1088/0004-637X/807/2/128

ABSTRACT We present high-resolution 870 m 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 m 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 >4 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.