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Published February 2012 | Published
Journal Article Open

Deep 1.1 mm-wavelength imaging of the GOODS-S field by AzTEC/ASTE – II. Redshift distribution and nature of the submillimetre galaxy population

Abstract

We report the results of the counterpart identification and a detailed analysis of the physical properties of the 48 sources discovered in our deep 1.1-mm wavelength imaging survey of the Great Observatories Origins Deep Survey-South (GOODS-S) field using the AzTEC instrument on the Atacama Submillimeter Telescope Experiment. One or more robust or tentative counterpart candidate is found for 27 and 14 AzTEC sources, respectively, by employing deep radio continuum, Spitzer/Multiband Imaging Photometer for Spitzer and Infrared Array Camera, and Large APEX Bolometer Camera 870 μm data. Five of the sources (10 per cent) have two robust counterparts each, supporting the idea that these galaxies are strongly clustered and/or heavily confused. Photometric redshifts and star formation rates (SFRs) are derived by analysing ultraviolet(UV)-to-optical and infrared(IR)-to-radio spectral energy distributions (SEDs). The median redshift of z_(med)∼ 2.6 is similar to other earlier estimates, but we show that 80 per cent of the AzTEC–GOODS sources are at z≥ 2, with a significant high-redshift tail (20 per cent at z≥ 3.3). Rest-frame UV and optical properties of AzTEC sources are extremely diverse, spanning 10 mag in the i- and K-band photometry (a factor of 10^4 in flux density) with median values of i= 25.3 and K= 22.6 and a broad range of red colour (i−K= 0–6) with an average value of i−K ≈ 3. These AzTEC sources are some of the most luminous galaxies in the rest-frame optical bands at z≥ 2, with inferred stellar masses M_*= (1–30) × 10^(10) M_⊙ and UV-derived SFRs of SFRUV≳ 10^(1-3) M_⊙ yr^(−1). The IR-derived SFR, 200–2000 M_⊙ yr^(−1), is independent of z or M_*. The resulting specific star formation rates, SSFR ≈ 1–100 Gyr^(−1), are 10–100 times higher than similar mass galaxies at z= 0, and they extend the previously observed rapid rise in the SSFR with redshift to z = 2–5. These galaxies have a SFR high enough to have built up their entire stellar mass within their Hubble time. We find only marginal evidence for an active galactic nucleus (AGN) contribution to the near-IR and mid-IR SEDs, even among the X-ray detected sources, and the derived M_* and SFR show little dependence on the presence of an X-ray bright AGN.

Additional Information

© 2011 The Authors. Monthly Notices of the Royal Astronomical Society © 2011 RAS. Accepted 2011 September 27. Received 2011 September 11; in original form 2011 June 6. Article first published online: 30 Dec 2011. The authors would like to thank M. Dickinson and R.-R. Chary for use of the Spitzer GOODS-S IRAC/MIPS catalogues. This work has also benefited from valuable discussions with C. Carilli, E. Chapin, R. Ivison, A. Pope, D. Sanders, N. Scoville and many others. We would also like to thank everyone who helped staff and support the AzTEC/ASTE 2007 operations, including K. Tanaka, M. Tashiro, K. Nakanishi, T. Tsukagoshi, M. Uehara, S. Doyle, P. Horner, J. Cortes, J. Karakla and G. Wallace. Support for this work was provided in part by the National Science Foundation grants AST-0838222 and AST-0907952.

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