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Published May 1, 2013 | Published
Journal Article Open

New Constraints on Cosmic Reionization from the 2012 Hubble Ultra Deep Field Campaign

Abstract

Understanding cosmic reionization requires the identification and characterization of early sources of hydrogen-ionizing photons. The 2012 Hubble Ultra Deep Field (UDF12) campaign has acquired the deepest infrared images with the Wide Field Camera 3 aboard Hubble Space Telescope and, for the first time, systematically explored the galaxy population deep into the era when cosmic microwave background (CMB) data indicate reionization was underway. The UDF12 campaign thus provides the best constraints to date on the abundance, luminosity distribution, and spectral properties of early star-forming galaxies. We synthesize the new UDF12 results with the most recent constraints from CMB observations to infer redshift-dependent ultraviolet (UV) luminosity densities, reionization histories, and electron scattering optical depth evolution consistent with the available data. Under reasonable assumptions about the escape fraction of hydrogen-ionizing photons and the intergalactic medium clumping factor, we find that to fully reionize the universe by redshift z ~ 6 the population of star-forming galaxies at redshifts z ~ 7-9 likely must extend in luminosity below the UDF12 limits to absolute UV magnitudes of M UV ~ –13 or fainter. Moreover, low levels of star formation extending to redshifts z ~ 15-25, as suggested by the normal UV colors of z ≃ 7-8 galaxies and the smooth decline in abundance with redshift observed by UDF12 to z ≃ 10, are additionally likely required to reproduce the optical depth to electron scattering inferred from CMB observations.

Additional Information

© 2013 American Astronomical Society. Received 2013 January 6; accepted 2013 March 19; published 2013 April 16. We thank Gary Hinshaw and David Larson for pointing us to the MCMC chains used in inferring the WMAP nine-year cosmological constraints. B.E.R. is supported by Steward Observatory and the University of Arizona College of Science. S.R.F. is partially supported by the David and Lucile Packard Foundation. US authors acknowledge financial support from the Space Telescope Science Institute under award HST-GO-12498.01-A. R.J.M. acknowledges the support of the European Research Council via the award of a Consolidator Grant, and the support of the Leverhulme Trust via the award of a Philip Leverhulme research prize. J.S.D. and R.A.A.B. acknowledge the support of the European Research Council via the award of an Advanced Grant to J.S.D. J.S.D. also acknowledges the support of the Royal Society via a Wolfson Research Merit award. A.B.R. and E.F.C.L. acknowledge the support of the UK Science & Technology Facilities Council. S.C. acknowledges the support of the European Commission through the Marie Curie Initial Training Network ELIXIR. This work is based in part 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 NAS5-26555.

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August 22, 2023
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