Capak, P. and Mobasher, B. and Scoville, N. Z. and McCracken, H. and Ilbert, O. and Salvato, M. and Menéndez-Delmestre, K. and Aussel, H. and Carilli, C. and Civano, F. and Elvis, M. and Giavalisco, M. and Jullo, E. and Kartaltepe, J. and Leauthaud, A. and Koekemoer, A. M. and Kneib, J.-P. and LeFloch, E. and Sanders, D. B. and Schinnerer, E. and Shioya, Y. and Shopbell, P. and Tanaguchi, Y. and Thompson, D. and Willott, C. J. (2011) Spectroscopy of Luminous z > 7 Galaxy Candidates and Sources of Contamination in z > 7 Galaxy Searches. Astrophysical Journal, 730 (2). Art. No. 68. ISSN 0004-637X. http://resolver.caltech.edu/CaltechAUTHORS:20110413-081502578
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We present three bright z ^+-dropout candidates selected from deep near-infrared (NIR) imaging of the COSMOS 2 deg^2 field. All three objects match the 0.8-8 μm colors of other published z > 7 candidates but are 3 mag brighter, facilitating further study. Deep spectroscopy of two of the candidates covering 0.64-1.02 μm with Keck-DEIMOS and all three covering 0.94-1.10 μm and 1.52-1.80 μm with Keck-NIRSPEC detects weak spectral features tentatively identified as Lyα at z = 6.95 and z = 7.69 in two of the objects. The third object is placed at z ~ 1.6 based on a 24 μm and weak optical detection. A comparison with the spectral energy distributions of known z < 7 galaxies, including objects with strong spectral lines, large extinction, and large systematic uncertainties in the photometry, yields no objects with similar colors. However, the λ > 1 μm properties of all three objects can be matched to optically detected sources with photometric redshifts at z ~ 1.8, so the non-detection in the i ^+ and z ^+ bands is the primary factor which favors a z > 7 solution. If any of these objects are at z ~ 7, the bright end of the luminosity function is significantly higher at z > 7 than suggested by previous studies, but consistent within the statistical uncertainty and the dark matter halo distribution. If these objects are at low redshift, the Lyman break selection must be contaminated by a previously unknown population of low-redshift objects with very strong breaks in their broadband spectral energy distributions and blue NIR colors. The implications of this result on luminosity function evolution at high redshift are discussed. We show that the primary limitation of z > 7 galaxy searches with broad filters is the depth of the available optical data.
|Additional Information:||© 2011 American Astronomical Society. Received 2009 October 1; accepted 2010 December 26; published 2011 March 7. Based on observations with the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration and made possible by the generous financial support of the W. M. Keck Foundation; the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA; the Canada–France–Hawaii Telescope with WIRCam, a joint project of CFHT, Taiwan, Korea, Canada, France, at the Canada–France–Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institute National des Sciences de l’Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii; the United Kingdom Infrared Telescope operated by the Joint Astronomy Centre on behalf of the Science and Technology Facilities Council of the U.K; the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan; the Canada–France–Hawaii Telescope with MegaPrime/MegaCam operated as a joint project by the CFHT Corporation, CEA/DAPNIA, the National Research Council of Canada, the Canadian Astronomy Data Centre, the Centre National de la Recherche Scientifique de France, TERAPIX and the University of Hawaii; the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA Inc., under NASA contract NAS5-26555; the XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA; the Chandra X-ray Observatory, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of the National Aeronautics Space Administration under contract NAS8-03060; the National Radio Astronomy Observatory which is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.; the 30 m telescope of the Institute for Radioastronomy at Millimeter Wavelengths (IRAM), which is funded by the German Max-Planck-Society, the French CNRS, and the Spanish National Geographical Institute. The authors recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Support for this work was provided by the Spitzer Science Center which is operated by the Jet Propulsion Laboratory (JPL), California Institute of Technology under NASA contract 1407, NASA through contract 1278386 issued by the JPL and NASA grant HST-GO- 09822. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech. This research has made use of the NASA/ IPAC Infrared Science Archive, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. H.J.M. and J.P.K. acknowledge support from the French Agene National de la Recheche fund ANR-07-BLAN-0228 as well as from CNES and the Programme National Cosmologie et Galaxies. P.C. acknowledges the Keck remote observing staff who allowed him to simultaneously attend the NIRSPEC observations and the birth of his daughter.|
|Subject Keywords:||galaxies: evolution; galaxies: formation; galaxies: high-redshift|
|Classification Code:||PACS: 98.62.Ai; 98.62.Qz; 98.62.Py; 95.30.Ky|
|Official Citation:||Spectroscopy of Luminous z > 7 Galaxy Candidates and Sources of Contamination in z > 7 Galaxy Searches P. Capak, B. Mobasher, N. Z. Scoville, H. McCracken, O. Ilbert, M. Salvato, K. Menéndez-Delmestre, H. Aussel, C. Carilli, F. Civano, M. Elvis, M. Giavalisco, E. Jullo, J. Kartaltepe, A. Leauthaud, A. M. Koekemoer, J.-P. Kneib, E. LeFloch, D. B. Sanders, E. Schinnerer, Y. Shioya, P. Shopbell, Y. Tanaguchi, D. Thompson and C. J. Willott doi: 10.1088/0004-637X/730/2/68|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||13 Apr 2011 18:30|
|Last Modified:||06 Jul 2015 20:02|
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