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

J. L. Wardlow, Ian Smail, Kristen 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

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Abstract

[abridged] We derive photometric redshifts from 17-band optical to mid-IR photometry of 74 robust counterparts to 68 of the 126 submillimetre galaxies (SMGs) selected at 870um by LABOCA observations in the ECDFS. The median photometric redshift of identified SMGs is z=2.2\pm0.1, the interquartile range is z=1.8-2.7 and we identify 10 (~15%) high-redshift (z>3) SMGs. We derive a simple redshift estimator for SMGs based on the 3.6 and 8um fluxes, which is accurate to Delta_z~0.4 for SMGs at z 3 and hence ~30% of all SMGs have z>3. We estimate that the full S_870um>4mJy SMG population has a median redshift of 2.5\pm0.6. In contrast to previous suggestions we find no significant correlation between S_870um and redshift. The median stellar mass of the SMGs derived from SED fitting is (9.2\pm0.9)x10^10Msun and the interquartile range is (4.7-14)x10^10Msun, although we caution that uncertainty in the star-formation histories results in a factor of ~5 uncertainty in these stellar masses. The median characteristic dust temperature of SMGs is 35.9\pm1.4K and the interquartile range is 28.5-43.3K. The infrared luminosity function shows that SMGs at z=2-3 typically have higher far-IR 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~2. The maximum contribution of bright SMGs to the global SFRD (~5% for SMGs with S_870um>4mJy; ~50% for SMGs with S_870um>1mJy) also occurs at z~2.
Original languageEnglish
Pages (from-to)1479-1508
JournalMonthly Notices of the Royal Astronomical Society
Volume415
Issue number2
DOIs
Publication statusPublished - 2011

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