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Published February 1, 2010 | Published
Journal Article Open

A Multiwavelength Study of a Sample of 70 μm Selected Galaxies in the COSMOS Field. I. Spectral Energy Distributions and Luminosities


We present a large robust sample of 1503 reliable and unconfused 70 μm selected sources from the multiwavelength data set of the Cosmic Evolution Survey. Using the Spitzer IRAC and MIPS photometry, we estimate the total infrared (IR) luminosity, L_(IR) (8-1000 μm), by finding the best-fit template from several different template libraries. The long-wavelength 70 and 160 μm data allow us to obtain a reliable estimate of L_(IR), accurate to within 0.2 and 0.05 dex, respectively. The 70 μm data point enables a significant improvement over the luminosity estimates possible with only a 24 μm detection. The full sample spans a wide range in IR luminosity, L_(IR) ≈ 10^8-10^(14) L_☉, with a median luminosity of 10^(11.4) L_☉. We identify a total of 687 luminous, 303 ultraluminous, and 31 hyperluminous infrared galaxies (LIRGs, ULIRGs, and HyLIRGs) over the redshift range 0.01 < z < 3.5 with a median redshift of 0.5. Presented here are the full spectral energy distributions (SEDs) for each of the sources compiled from the extensive multiwavelength data set from the ultraviolet (UV) to the far-infrared. A catalog of the general properties of the sample (including the photometry, redshifts, and L_(IR)) is included with this paper. We find that the overall shape of the SED and trends with L_(IR) (e.g., IR color temperatures and optical-IR ratios) are similar to what has been seen in studies of local objects; however, our large sample allows us to see the extreme spread in UV to near-infrared colors spanning nearly 3 orders of magnitude. In addition, using SED fits we find possible evidence for a subset of cooler ultraluminous objects than observed locally. However, until direct observations at longer wavelengths are obtained, the peak of emission and the dust temperature cannot be well constrained. We use these SEDs, along with the deep radio and X-ray coverage of the field, to identify a large sample of candidate active galactic nuclei (AGNs). We find that the fraction of AGNs increases strongly with L_(IR), as it does in the local universe, and that nearly 70% of ULIRGs and all HyLIRGs likely host a powerful AGN.

Additional Information

© 2010 American Astronomical Society. Print publication: Issue 2 (2010 February 1); received 2009 July 14; accepted for publication 2009 November 25; published 2010 January 6. Support for this work was provided in part by NASA through contracts 1282612, 1298213, and 1344920 issued by the Jet Propulsion Laboratory. We would also like to recognize the contributions from all of the members of the COSMOS Team who helped in obtaining and reducing the large amount of multiwavelength data that are now publicly available through theNASA Infrared Science Archive (IRSA) at http://irsa.ipac.caltech.edu/Missions/cosmos.html. The analysis pipeline used to reduce the DEIMOS data was developed at UC Berkeley with support from NSF grant AST-0071048. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This research has also made use of data from the Sloan Digital Sky Survey (SDSS-DR7). Funding for the SDSS and SDSSII has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the JapaneseMonbukagakusho, theMax Planck Society, and theHigher Education Funding Council for England. The SDSS Web site is http://www.sdss.org/.

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Published - Kartaltepe2010p6998Astrophys_J.pdf


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