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

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

Abstract

We derive photometric redshifts from 17-band optical to mid-infrared photometry of 78 robust radio, 24-μm and Spitzer IRAC counterparts to 72 of the 126 submillimetre galaxies (SMGs) selected at 870 μm 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 σz= 0.9 and we identify 11 (∼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 ∼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 ∼15 per cent of all the SMGs are below the flux limits of our IRAC observations and thus may lie at z≳ 3 and hence at most ∼30 per cent of all SMGs have z≳ 3. We estimate that the full S870 μm > 4 mJy 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) × 1010 M⊙ although we caution that the uncertainty in the star formation histories results in a factor of ∼5 uncertainty in these stellar masses. Using a single temperature modified blackbody fit with β= 1.5, the median characteristic dust temperature of SMGs is 37.4 ± 1.4 K. 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∼ 2. The maximum contribution of bright SMGs to the global SFRD (∼5 per cent for SMGs with S870 μm≳ 4 mJy or ∼50 per cent extrapolated to SMGs with S870 μm > 1 mJy) also occurs at z∼ 2.

Citation

Wardlow, J., Smail, I., Coppin, K., Alexander, D., Brandt, W., Danielson, A., …van der Werf, P. (2011). 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(2), 1479-1508. https://doi.org/10.1111/j.1365-2966.2011.18795.x

• Journal Article Type: Article
• Publication Date: Aug 1, 2011
• Deposit Date: Jan 25, 2012
• Publicly Available Date: Feb 19, 2015
• Journal: Monthly Notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Electronic ISSN: 1365-2966
• Publisher: Royal Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 415
• Issue: 2
• Pages: 1479-1508
• DOI: https://doi.org/10.1111/j.1365-2966.2011.18795.x
• Keywords: Galaxies: evolution, Galaxies: high-redshift, Galaxies: starburst, Submillimetre: galaxies.