University of Hertfordshire

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From the same journal

By the same authors

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

Research output: Contribution to journalArticlepeer-review


  • James Simpson
  • Ian Smail
  • Mark Swinbank
  • Scott Chapman
  • Rob Ivison
  • Alasdair Thomson
  • Itziar Aretxaga
  • Andrew Blain
  • Will Cowley
  • Chian-Chou Chen
  • Jim Dunlop
  • Alastair Edge
  • Duncan Farrah
  • Edo Ibar
  • Alex Karim
  • Kirsten Knudsen
  • Rowin Meijerink
  • Michal Michalowski
  • Douglas Scott
  • Marco Spanns
  • Paul van der Werf
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Original languageEnglish
Article number128
Number of pages13
JournalThe Astrophysical Journal
Publication statusPublished - 10 Jul 2015


We present high-resolution 870-um ALMA continuum maps of 30 bright sub-millimeter sources in the UKIDSS UDS field. These sources are selected from deep, 1-square degrees 850-um maps from the SCUBA--2 Cosmology Legacy Survey, and are representative of the brightest sources in the field (median SCUBA2 flux S_850=8.7+/-0.4 mJy). We detect 52 sub-millimeter galaxies (SMGs) at >4-sigma significance in our 30 ALMA maps. In 61+/-17% 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 L_IR>10^12 Lo. The brightest SMG contributes on average 80+/-4% of the single-dish flux density, and in the ALMA maps containing >=2 SMGs the secondary SMG contributes 25+/-3% of the integrated ALMA flux. We construct source counts and show that multiplicity boosts the apparent single-dish cumulative counts by 20% at S_870>7.5mJy, and by 60% at S_870>12mJy. 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+/-0.6mJy. The break corresponds to a luminosity of ~6x10^12Lsol or a star-formation rate of ~1000Mo/yr. For the typical sizes of these SMGs, which are resolved in our ALMA data with r=1.2+/-0.1kpc, this yields a limiting SFR density of ~100Msol/yr/kpc2. Finally, the number density of S_870>2mJy 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 must be physically associated.


J. M. Simpson, et al., “The SCUBA-2 Cosmology Legacy Survey: ALMA resolves the bright-end of the sub-millimetre number counts”, The Astrophysical Journal, Vol. 807(2), July 2015. © 2015. The American Astronomical Society.

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