Cosmological Parameter Estimation Using 21 cm Radiation from the Epoch of Reionization

A number of radio interferometers are currently being planned or constructedto observe 21 cm emission from reionization. Not only will such measurementsprovide a detailed view of that epoch, but, since the 21 cm emission alsotraces the distribution of matter in the Universe, this signal can be used toconstrain cosmological parameters at 6 < z < 20. The sensitivity of aninterferometer to the cosmological information in the signal may depend on howprecisely the angular dependence of the 21 cm 3-D power spectrum can bemeasured. Utilizing an analytic model for reionization, we quantify all theeffects that break the spherical symmetry of the 3-D 21 cm power spectrum andproduce physically motivated predictions for this power spectrum. We find thatupcoming observatories will be sensitive to the 21 cm signal over a wide rangeof scales, from larger than 100 to as small as 1 comoving Mpc. We considerthree methods to measure cosmological parameters from the signal: (1) directfitting of the density power spectrum to the signal, (2) using only thevelocity field fluctuations in the signal, (3) looking at the signal at largeenough scales such that all fluctuations trace the density field. With theforemost method, the first generation of 21 cm observations should moderatelyimprove existing constraints on cosmological parameters for certainlow-redshift reionization scenarios, and a two year observation with the secondgeneration interferometer MWA5000 can improve constraints on Omega_w, Omega_mh^2, Omega_b h^2, Omega_nu, n_s, and alpha_s. If the Universe is substantiallyionized by z = 12 or if spin temperature fluctuations are important, we showthat it will be difficult to place competitive constraints on cosmologicalparameters with any of the considered methods.Comment: 20 pages, 12 figures, accepted by Ap