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Published April 20, 2011 | Published
Journal Article Open

The Redshift and Nature of AzTEC/COSMOS 1: A Starburst Galaxy at z = 4.6


Based on broadband/narrowband photometry and Keck DEIMOS spectroscopy, we report a redshift of z = 4.64^(+0.06)_(–0.08) for AzTEC/COSMOS 1, the brightest submillimeter galaxy (SMG) in the AzTEC/COSMOS field. In addition to the COSMOS-survey X-ray to radio data, we report observations of the source with Herschel/PACS (100, 160 μm), CSO/SHARC II (350 μm), and CARMA and PdBI (3 mm). We do not detect CO(5 → 4) line emission in the covered redshift ranges, 4.56-4.76 (PdBI/CARMA) and 4.94-5.02 (CARMA). If the line is within this bandwidth, this sets 3σ upper limits on the gas mass to ≲8 × 10^9 M_☉ and ≲5 × 10^(10) M_☉, respectively (assuming similar conditions as observed in z ~ 2 SMGs). This could be explained by a low CO-excitation in the source. Our analysis of the UV-IR spectral energy distribution of AzTEC 1 shows that it is an extremely young (≲50 Myr), massive (M * ~ 10^(11) M_☉), but compact (≲2 kpc) galaxy, forming stars at a rate of ~1300 M_☉ yr^(–1). Our results imply that AzTEC 1 is forming stars in a "gravitationally bound" regime in which gravity prohibits the formation of a superwind, leading to matter accumulation within the galaxy and further generations of star formation.

Additional Information

© 2011 American Astronomical Society. Received 2010 December 13; accepted 2011 February 15; published 2011 March 25. Based on observations with the W. M. Keck Observatory, the Canada–France–Hawaii Telescope, the United Kingdom Infrared Telescope, the Subaru Telescope, the NASA/ESA Hubble Space Telescope, the NASA Spitzer Telescope, the Caltech Sub-mm Observatory, the Smithsonian Millimeter Array, and the National Radio Astronomy Observatory. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. The authors acknowledge the significant cultural role that the summit of Mauna Kea has within the indigenous Hawaiian community; NASA grants HST-GO-09822 (contracts 1407, 1278386; SSC); HST-HF-51235.01 (contract NAS 5-26555; STScI); GO7-8136A; Blancheflor Boncompagni Ludovisi foundation (F.C.); French Agence National de la Recheche fund ANR-07-BLAN-0228; CNES; Programme National Cosmologie et Galaxies; UKF; DFG; DFG Leibniz Prize (FKZ HA 1850/28-1); European Union's Seventh Framework programme (grant agreement 229517); making use of the NASA/IPAC IRSA, by JPL/Caltech, under contract with the National Aeronautics and Space Administration; IRAM PdBI supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain); CARMA supported by the states of California, Illinois, and Maryland, the Gordon and Betty Moore Foundation, the Eileen and Kenneth Norris Foundation, the Caltech Associates, and NSF.

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