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. 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., …van der Werf, P. P. (2015). The SCUBA-2 Cosmology Legacy Survey: ALMA resolves the bright-end of the submillimeter number counts. Astrophysical Journal, 807(2), 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.
• Public URL: https://durham-repository.worktribe.com/output/1402460