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Cross-correlation studies between CMB temperature anisotropies and 21 cm fluctuations

Cooray, Asantha (2004) Cross-correlation studies between CMB temperature anisotropies and 21 cm fluctuations. Physical Review D, 70 (6). Art. No. 063509. ISSN 0556-2821.

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During the transition from a neutral to a fully reionized universe, scattering of cosmic microwave background (CMB) photons via free electrons leads to a new anisotropy contribution to the temperature distribution. If the reionization process is inhomogeneous and patchy, the era of reionization is also visible via brightness temperature fluctuations in the redshifted 21 cm line emission from neutral hydrogen. Since regions containing electrons and neutral hydrogen are expected to trace the same underlying density field, the two are (anti)correlated and this is expected to be reflected in the anisotropy maps via a correlation between arcminute-scale CMB temperature and the 21 cm background. In terms of the angular cross-power spectrum, unfortunately, this correlation is insignificant due to a geometric cancellation associated with second-order CMB anisotropies. The same cross correlation between ionized and neutral regions, however, can be studied using a bispectrum involving large-scale velocity field of ionized regions from the Doppler effect, arcminute-scale CMB anisotropies during reionization, and the 21 cm background. While the geometric cancellation is partly avoided, the signal-to-noise ratio related to this bispectrum is reduced due to the large cosmic variance related to velocity fluctuations traced by the Doppler effect. Unless the velocity field during reionization can be independently established, it is unlikely that the correlation information related to the relative distribution of ionized electrons and regions containing neutral hydrogen can be obtained with a combined study involving CMB and 21 cm fluctuations.

Item Type:Article
Additional Information:©2004 The American Physical Society. Received 26 May 2004; published 7 September 2004. This work was supported in part by DOE DE-FG03-92-ER40701.
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ID Code:10989
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Deposited On:21 Jun 2008
Last Modified:26 Dec 2012 10:07

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