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Published April 30, 2009 | Published
Journal Article Open

A submillimetre galaxy at z= 4.76 in the LABOCA survey of the Extended Chandra Deep Field-South


We report on the identification of the highest redshift submillimetre-selected source currently known LESS J033229.4−275619. This source was detected in the Large Apex Bolometer Camera (LABOCA) Extended Chandra Deep Field-South (ECDF-S) Submillimetre Survey (LESS), a sensitive 870-μm survey (σ_(870 μm)∼ 1.2 mJy) of the full 30 × 30 arcmin_2 ECDF-S with the LABOCA on the Atacama Pathfinder Experiment telescope. The submillimetre emission is identified with a radio counterpart for which optical spectroscopy provides a redshift of z= 4.76 . We show that the bolometric emission is dominated by a starburst with a star formation rate of ∼1000 M_⊙ yr^(−1), although we also identify a moderate luminosity active galactic nucleus (AGN) in this galaxy. Thus it has characteristics similar to those of z∼ 2 submillimetre galaxies (SMGs), with a mix of starburst and obscured AGN signatures. This demonstrates that ultraluminous starburst activity is not just restricted to the hosts of the most luminous (and hence rare) quasi-stellar objects at z∼ 5 , but was also occurring in less extreme galaxies at a time when the Universe was less than 10 per cent of its current age. Assuming that we are seeing the major phase of star formation in this galaxy, then we demonstrate that it would be identified as a luminous distant red galaxy at z∼ 3 and that the current estimate of the space density of z > 4 SMGs is only sufficient to produce ≳10 per cent of the luminous red galaxy population at these early times. However, this leaves open the possibility that some of these galaxies formed through less intense, but more extended star formation events. If the progenitors of all of the luminous red galaxies at z∼ 3 go through an ultraluminous starburst at z≳ 4 then the required volume density of z > 4 SMGs will exceed that predicted by current galaxy formation models by more than an order of magnitude.

Additional Information

© 2009 RAS. Accepted 2009 February 23. Received 2009 February 23; in original form 2009 January 25. We would like to thank an anonymous referee for helpful comments and suggestions on the paper. We thank John Helly for help with extracting information from the Millenium and GALFORM data bases. KEKC acknowledges support from a Science and Technology Facilities Council (STFC) fellowship. IRS, DMA and JSD acknowledge support from the Royal Society. JEG and JLW acknowledge support from the STFC, and AMS acknowledges support from a Lockyer fellowship. The work of DS was carried out at Jet Propulsion Laboratory (JPL), California Institute of Technology (Caltech), under a contract with National Aeronautics and Space Administration (NASA). WNB acknowledges support from the Chandra X-ray Observatory's grant SP8-9003A. Observations have been carried out using APEX and the VLT under Program IDs: 080.A-3023, 079.F-9500, 170.A-0788, 074.A-0709 and 275.A-5060. APEX is operated by the Max-Planck-Institut für Radioastronomie, the European Southern Observatory and the Onsala Space Observatory.We would like to thank the staff for their aid in carrying out the observations. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among Caltech, the University of California and NASA. The Keck Observatory was made possible by the generous financial support of the W. M. Keck Foundation. This work is based in part on observations from the Legacy Science Program, made with the Spitzer Space Telescope, which is operated by JPL, Caltech, under a contract with NASA; and support for this work was provided by NASA through an award issued by JPL/Caltech. This research has also made use of the NASA/IPAC Extragalactic Database (NED) which is operated by JPL/Caltech, under contract with NASA. Ned Wright's Javascript Cosmology Calculator was also used in preparing this paper (Wright 2006).

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August 20, 2023
August 20, 2023