Journal Article

The impact of H <span class="smallCaps">i</span> in galaxies on 21-cm intensity fluctuations during the reionization epoch

J. S. B. Wyithe, L. Warszawski, P. M. Geil and S. Peng Oh

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 395, issue 1, pages 311-318
Published in print May 2009 | ISSN: 0035-8711
Published online April 2009 | e-ISSN: 1365-2966 | DOI:
The impact of H i in galaxies on 21-cm intensity fluctuations during the reionization epoch

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We investigate the impact of neutral hydrogen (H i) in galaxies on the statistics of 21-cm fluctuations using seminumerical modelling. Following the reionization of hydrogen, the H i content of the Universe is dominated by damped absorption systems (DLAs), with a cosmic density in H i that is observed to be constant at a level equal to ∼2 per cent of the cosmic baryon density from z∼ 1 to z∼ 5. We show that extrapolation of this constant fraction into the reionization epoch results in a reduction in the amplitude of 21-cm fluctuations over a range of spatial scales. We further find that consideration of H i in galaxies/DLAs reduces the prominence of the H ii region induced shoulder in the 21-cm power spectrum (PS), and hence modifies the scale dependence of 21-cm fluctuations. We also estimate the 21-cm–galaxy cross PS and show that the cross PS changes sign on scales corresponding to the H ii regions. From consideration of the sensitivity for forthcoming low-frequency arrays, we find that the effects of H i in galaxies/DLAs on the statistics of 21-cm fluctuations will be significant with respect to the precision of a PS or cross PS measurement. In addition, since overdense regions are reionized first we demonstrate that the cross-correlation between galaxies and 21-cm emission changes sign at the end of the reionization era, providing an alternative avenue to pinpoint the end of reionization. The sum of our analysis indicates that the H i content of the galaxies that reionize the universe will need to be considered in detailed modelling of the 21-cm intensity PS in order to correctly interpret measurements from forthcoming low-frequency arrays.

Keywords: galaxies: high-redshift; intergalactic medium; cosmology: theory; diffuse radiation; large-scale structure of Universe

Journal Article.  6376 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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