We construct a simple but self-consistent analytic ionization model for rapid exploration of 21 cm power spectrum observables in redshift space. It is fully described by the average ionization fraction xe(z) and H II patch size R(z) and has the flexibility to accommodate various reionization scenarios. The model associates ionization regions with dark matter halos of the number density required to recover xe and treats redshift space distortions self-consistently with the virial velocity of such halos. Based on this model, we study the line-of-sight structures in the brightness fluctuations, since they are the most immune to foreground contamination. We explore the degeneracy between the H II patch size and nonlinear redshift space distortion in the one-dimensional power spectrum. We also discuss the limitations experimental frequency and angular resolutions place on their distinguishability. Angular resolution dilutes even the radial signal and will be a serious limitation for resolving small bubbles before the end of reionization. Nonlinear redshift space distortions suggest that a resolution of the order of 1"-10" and a frequency resolution of 10 kHz will ultimately be desirable to extract the full information in the radial field at z~10. First-generation instruments such as LOFAR and MWA could potentially measure radial H II patches of a few comoving megaparsecs and larger at the end of reionization and are unlikely to be affected by nonlinear redshift space distortions.
The Astrophysical Journal
- Pub Date:
- June 2006
- Cosmology: Theory;
- Cosmology: Diffuse Radiation;
- Methods: Analytical;
- 13 pages, 10 figures. Revised version. Includes minor changes. Adds appendix on accomodating a distribution of radii for the HII regions. Accepted for publication in ApJ