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

Date

2010-06-10

Authors

Wardlow, J. L.
Smail, Ian
Coppin, K. E. K.
Alexander, D. M.
Brandt, W. N.
Danielson, A. L. R.
Luo, B.
Swinbank, A. M.
Walter, F.
Weiss, A.

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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 z3 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.

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Wardlow, J. L., Ian Smail, K. E. K. Coppin, D. M. Alexander, et al. 2010. "The LABOCA survey of the Extended Chandra Deep Field South: A photometric redshift survey of submillimetre galaxies." Monthly Notices of the Royal Astronomical Society 415:1479.

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