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Galaxies at z= 6–9 from the WFC3/IR imaging of the Hubble Ultra Deep Field

McLure, R. J. and Dunlop, J. S. and Cirasuolo, M. and Koekemoer, A. M. and Sabbi, E. and Stark, D. P. and Targett, T. A. and Ellis, R. S. (2010) Galaxies at z= 6–9 from the WFC3/IR imaging of the Hubble Ultra Deep Field. Monthly Notices of the Royal Astronomical Society, 403 (2). pp. 960-983. ISSN 0035-8711.

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We present the results of a systematic search for galaxies in the redshift range z = 6–9 , within the new, deep, near-infrared (Y, J, H) imaging of the Hubble Ultra Deep Field provided by the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope. We have performed full spectral energy distribution fitting to the optical+infrared photometry of all high-redshift galaxy candidates detected at ≥5σ significance in at least one of the WFC3/IR broad-band filters. After careful rejection of contaminants, the result is a sample of 49 galaxies with primary photometric redshift solutions z > 5.9, within the 4.5 arcmin^2 field covered by the new near-infrared imaging. Our sample, selected without recourse to specific colour cuts, reselects all but the faintest one of the 16 z_(850)-drops selected by Oesch et al., recovers all five of the Y_(105)-drops reported by Bouwens et al. and adds a further 29 equally plausible galaxy candidates, of which 12 lie beyond z ≃ 6.3 and four lie beyond z ≃ 7.0. However, we also present confidence intervals on our photometric redshift estimates, including alternative secondary redshift solutions. As a result of this analysis, we caution that acceptable low-redshift (z < 2) solutions exist for 28 out of the 37 galaxies at z > 6.3 and in particular for all eight of the galaxy candidates reported here at z > 7.5. Nevertheless, we note that the very highest redshift candidates appear to be strongly clustered in the field. Based on our photometric redshift analysis, we derive new estimates of the ultraviolet galaxy luminosity function at z ≃ 7 and 8. Where our results are most robust, at a characteristic luminosity M_(1500) ≃ −19.5 (AB), we find that the comoving number density of galaxies declines by a factor of ≃2.5 between z ≃ 6 and 7 and by a further factor of ≃2 by z ≃ 8. These results suggest that it is difficult for the observed population of high-redshift star-forming galaxies to achieve reionization by z ≃ 6 without a significant contribution from galaxies well below the detection limits, plus alterations in the escape fraction of ionizing photons and/or continued vigorous star formation at z > 15 .

Item Type:Article
Related URLs:
URLURL TypeDescription
Koekemoer, A. M.0000-0002-6610-2048
Sabbi, E.0000-0003-2954-7643
Ellis, R. S.0000-0001-7782-7071
Additional Information:© 2010 The Authors. Journal compilation © 2010 RAS. Accepted 2009 December 4. Received 2009 December 4; in original form 2009 September 15. The authors would like to thank the anonymous referee whose comments and suggestions significantly improved the final version of this manuscript. This work is based primarily on observations made with the NASA/ESA HST, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. 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 NASA contract 1407. RJM and JSD acknowledge the support of the Royal Society through a University Research Fellowship and a Wolfson Research Merit award, respectively. MC and DPS acknowledge the support of STFC through the award of an Advanced Fellowship and Post-Doctoral Fellowship, respectively. TAT acknowledges the support of NSERC.
Funding AgencyGrant Number
Science and Technology Facilities Council (STFC)UNSPECIFIED
Natural Sciences and Engineering Research Council of Canada (NSERC)UNSPECIFIED
Subject Keywords:galaxies: evolution; galaxies: formation; galaxies: high-redshift; cosmology: observations
Issue or Number:2
Record Number:CaltechAUTHORS:20100414-093509270
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:17971
Deposited By: Jason Perez
Deposited On:14 Apr 2010 21:34
Last Modified:14 Dec 2019 05:10

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