Wednesday, August 22, 2012

1208.4277 (Sebastien Clesse et al.)

Background reionization history from omniscopes    [PDF]

Sebastien Clesse, Laura Lopez-Honorez, Christophe Ringeval, Hiroyuki Tashiro, Michel Tytgat
The measurements of the 21 cm brightness temperature fluctuations from the neutral hydrogen at the epoch of reionization (EoR) should inaugurate the next generation of cosmological observables. In this respect, many works have concentrated on the disambiguation of the cosmological signals from the dominant reionization foregrounds. However, even after perfect foregrounds removal, our ignorance on the background reionization history can significantly affect the cosmological parameter estimation. In particular, the interdependence between the hydrogen ionized fraction, the baryon density and the optical depth to the redshift of observation induce non-trivial degeneracies between the cosmological parameters that have not been considered so far. Using a simple, but consistent, reionization model, we revisit their expected constraints for a futuristic giant 21 cm omniscope by using for the first time Monte-Carlo-Markov-Chains (MCMC) methods on multi-redshift full sky simulated data. Our results agree well with the usual Fisher matrix analysis on the three-dimensional flat sky power spectrum but only when the above-mentioned degeneracies are kept under control. In the opposite situation, Fisher results can be inaccurate. We show that these conditions can be fulfilled by combining Cosmic Microwave Background measurements with multiple observation redshifts probing the beginning of EoR. This allows a precise reconstruction of the total optical depth, reionization duration and maximal spin temperature. Finally, we discuss the robustness of these results in presence of unresolved ionizing sources. Although most of the standard cosmological parameters remain weakly affected, we find a significant degradation of the background reionization parameter estimation in presence of nuisance ionizing sources.
View original: http://arxiv.org/abs/1208.4277

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