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A Hubble and Spitzer space telescope survey for gravitationally lensed galaxies: further evidence for a significant population of low-luminosity galaxies beyond z=7

Richard, Johan and Stark, Daniel P. and Ellis, Richard S. and George, Matthew R. and Egami, Eiichi and Kneib, Jean-Paul and Smith, Graham P. (2008) A Hubble and Spitzer space telescope survey for gravitationally lensed galaxies: further evidence for a significant population of low-luminosity galaxies beyond z=7. Astrophysical Journal, 685 (2). pp. 705-724. ISSN 0004-637X.

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We present the results of a systematic search for gravitationally lensed continuum Lyman break "dropouts" beyond a redshift 7 conducted via very deep imaging through six foreground clusters undertaken with the Hubble and Spitzer space telescopes. The survey has yielded 10 z-band and two J-band dropout candidates to photometric limits of J_(110) ≃ 26.2 AB (5 σ). Taking into account the magnifications afforded by our clusters (1-4 mag), we probe the presence of z > 7 sources to unlensed limits of J_(110) ≃ 30 AB, fainter than those charted in the Hubble Ultradeep Field. To verify the fidelity of our candidates we conduct a number of tests for instrumental effects which would lead to spurious detections, and carefully evaluate the likelihood of foreground contamination by considering photometric uncertainties in the dropout signature, the upper limits from stacked IRAC data and the statistics of multiply imaged sources. Overall, we conclude that we can expect about half of our sample of z-band dropouts to be at high redshift. An ambitious infrared spectroscopic campaign undertaken with the NIRSPEC spectrograph at the W. M. Keck Observatory for seven of the most promising candidates failed to detect any Lyα emission highlighting the challenge of making further progress in this field. While the volume density of high-redshift sources will likely remain uncertain until more powerful facilities are available, our data provides the first potentially interesting constraints on the UV luminosity function at z ≃ 7.5 at intrinsically faint limits. We discuss the implications of our results in the context of the hypothesis that the bulk of the reionizing photons in the era 7 < z < 12 arise in low-luminosity galaxies undetected by conventional surveys.

Item Type:Article
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URLURL TypeDescription
Richard, Johan0000-0001-5492-1049
Ellis, Richard S.0000-0001-7782-7071
Kneib, Jean-Paul0000-0002-4616-4989
Smith, Graham P.0000-0003-4494-8277
Additional Information:© 2008 The American Astronomical Society. Received 2008 March 31, accepted for publication 2008 June 24. We thank the anonymous referee for a report that has improved the content of this paper, and Rychard Bouwens for his very helpful comments on an earlier version of the manuscript. We also acknowledge discussions with Rodger Thompson, Elizabeth Stanway, Roser Pello, Daniel Schaerer, Kelle Cruz, and Adam Kraus. Andrew Blain and Naveen Reddy kindly provided the Keck NIRC observations of Abell 2218. We are thankful to Ichi Tanaka for his support in the reduction of MOIRCS imaging data. We acknowledge funding from NASA grant HST-GO-10504.01-A and Spitzer program GO-20439. 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. This program is based on observations made with the NASA/ESA Hubble Space Telescope, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555, the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan, the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA, and the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council of Canada, the Institut National des Sciences de l’Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii.
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Subject Keywords:cosmology: observations; galaxies: evolution; galaxies: formation; galaxies: high-redshift; gravitational lensing
Issue or Number:2
Record Number:CaltechAUTHORS:RICapj08
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:13571
Deposited By: Tony Diaz
Deposited On:08 May 2009 21:43
Last Modified:16 Nov 2019 00:42

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