Bowman, Judd D. and Rogers, Alan E. E. and Hewitt, Jacqueline N. (2008) Observing Neutral Hydrogen Above Redshift 6: The “Global” Perspective. In: The Evolution of Galaxies through the Neutral Hydrogen Window, Arecibo Observatory (Puerto Rico), 1–3 February 2008. American Institute of Physics Conference Proceedings (1035). American Institute of Physics , Melville, NY, pp. 87-89. ISBN 978-0-7354-0558-5 http://resolver.caltech.edu/CaltechAUTHORS:BOWaipcp08a
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Above redshift 6, the dominant source of neutral hydrogen in the Universe shifts from localized clumps in and around galaxies and filaments to a pervasive, diffuse component of the intergalactic medium (IGM). This transition tracks the global neutral fraction of hydrogen in the IGM and can be studied, in principle, through the redshifted 21 cm hyperfine transition line. During the last half of the reionization epoch, the mean (global) brightness temperature of the redshifted 21 cm emission is proportional to the neutral fraction, but at earlier times (10<z<25), the mean brightness temperature should probe the spin temperature of neutral hydrogen in the IGM. Measuring the (of order 10 mK) mean brightness temperature of the redshifted 21 cm line as a function of frequency (and hence redshift) would chart the early evolution of galaxies through the heating and ionizing of the IGM by their stellar populations. Experiments are already underway to accomplish this task or, at least, provide basic constraints on the evolution of the mean brightness temperature. We provide a brief overview of one of these projects, the Experiment to the Detect the Global EOR Signature (EDGES), and discuss prospects for future results.
|Item Type:||Book Section|
|Additional Information:||Copyright © 2008 American Institute of Physics. Issue Date: 1 August 2008. This work was supported by the Massachusetts Institute of Technology, School of Science, and by the NSF through grant AST-0457585. JDB is supported by NASA through Hubble Fellowship grant HF-01205.01-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555.|
|Subject Keywords:||cosmology, intergalactic matter, red shift, clusters of galaxies, cosmic background radiation, ionization, astronomical telescopes|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Archive Administrator|
|Deposited On:||25 Nov 2008 19:16|
|Last Modified:||26 Dec 2012 10:31|
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