The bispectrum of redshifted 21-cm fluctuations from the dark ages

Details The bispectrum of redshifted 21-cm fluctuations from the dark ages The bispectrum of redshifted 21-cm fluctuations from the dark ages

2006-11-03

arxiv.org/abs/astro-ph/0611126v2

Astrophys.J.662:1-14,2007

Astronomy and Astrophysics

Astrophysics

15 pages, 4 figures, revised version accepted for publication in ApJ (contains an improved discussion of gas temperature fluct

Scientific paper

10.1086/517963

Brightness-temperature fluctuations in the redshifted 21-cm background from the cosmic dark ages are generated by irregularities in the gas-density distribution and can then be used to determine the statistical properties of density fluctuations in the early Universe. We first derive the most general expansion of brightness-temperature fluctuations up to second order in terms of all the possible sources of spatial fluctuations. We then focus on the three-point statistics and compute the angular bispectrum of brightness-temperature fluctuations generated prior to the epoch of hydrogen reionization. For simplicity, we neglect redshift-space distortions. We find that low-frequency radio experiments with arcmin angular resolution can easily detect non-Gaussianity produced by non-linear gravity with high signal-to-noise ratio. The bispectrum thus provides a unique test of the gravitational instability scenario for structure formation, and can be used to measure the cosmological parameters. Detecting the signature of primordial non-Gaussianity produced during or right after an inflationary period is more challenging but still possible. An ideal experiment limited by cosmic variance only and with an angular resolution of a few arcsec has the potential to detect primordial non-Gaussianity with a non-linearity parameter of f_NL ~ 1. Additional sources of error as weak lensing and an imperfect foreground subtraction could severely hamper the detection of primordial non-Gaussianity which will benefit from the use of optimal estimators combined with tomographic techniques.

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