The LABOCA survey of the Extended Chandra Deep Field-South: a photometric redshift survey of submillimetre galaxies

J. L. Wardlow, Ian Smail, K. E. K. Coppin, D. M. Alexander, W. N. Brandt, A. L. R. Danielson, B. Luo, A. M. Swinbank, F. Walter, A. Weiss, Y. Q. Xue, S. Zibetti, F. Bertoldi, A. D. Biggs, S. C. Chapman, H. Dannerbauer, J. S. Dunlop, E. Gawiser, R. J. Ivison, K. K. KnudsenA. Kovacs, C. G. Lacey, K. M. Menten, N. Padilla, H. -W. Rix, P. P. van der Werf

Research output: Contribution to journalArticlepeer-review


We derive photometric redshifts from 17-band optical to mid-infrared photometry of 78 robust radio, 24-mu m and Spitzer IRAC counterparts to 72 of the 126 submillimetre galaxies (SMGs) selected at 870 mu m by LABOCA observations in the Extended Chandra Deep Field-South (ECDF-S). We test the photometric redshifts of the SMGs against the extensive archival spectroscopy in the ECDF-S. The median photometric redshift of identified SMGs is z = 2.2 +/- 0.1, the standard deviation is sigma(z) = 0.9 and we identify 11 (similar to 15 per cent) high-redshift (z >= 3) SMGs. A statistical analysis of sources in the error circles of unidentified SMGs identifies a population of possible counterparts with a redshift distribution peaking at z = 2.5 +/- 0.2, which likely comprises similar to 60 per cent of the unidentified SMGs. This confirms that the bulk of the undetected SMGs are coeval with those detected in the radio/mid-infrared. We conclude that at most similar to 15 per cent of all the SMGs are below the flux limits of our IRAC observations and thus may lie at z greater than or similar to 3 and hence at most similar to 30 per cent of all SMGs have z greater than or similar to 3. We estimate that the full S-870 mu m > 4mJy SMG population has a median redshift of 2.5 +/- 0.5. In contrast to previous suggestions, we find no significant correlation between submillimetre flux and redshift. The median stellar mass of the SMGs derived from spectral energy distribution fitting is (9.1 +/- 0.5) x 10(10)M(circle dot) although we caution that the uncertainty in the star formation histories results in a factor of similar to 5 uncertainty in these stellarmasses. Using a single temperature modified blackbody fit with beta = 1.5, the median characteristic dust temperature of SMGs is 37.4 +/- 1.4K. The infrared luminosity function shows that SMGs at z = 2-3 typically have higher far-infrared luminosities and luminosity density than those at z = 1-2. This is mirrored in the evolution of the star formation rate density (SFRD) for SMGs which peaks at z similar to 2. The maximum contribution of bright SMGs to the global SFRD (similar to 5 per cent for SMGs with S-870 mu m greater than or similar to 4mJy or similar to 50 per cent extrapolated to SMGs with S-870 mu m > 1mJy) also occurs at z similar to 2.

Original languageEnglish
Pages (from-to)1479-1508
Number of pages30
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Publication statusPublished - Aug 2011


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