21-cm fluctuations from inhomogeneous X-ray heating before reionization
Abstract
Many models of early structure formation predict a period of heating immediately preceding reionization, when X-rays raise the gas temperature above that of the cosmic microwave background. These X-rays are often assumed to heat the intergalactic medium (IGM) uniformly, but in reality will heat the gas more strongly closer to the sources. We develop a framework for calculating fluctuations in the 21-cm brightness temperature that originate from this spatial variation in the heating rate. High-redshift sources are highly clustered, leading to significant gas temperature fluctuations (with fractional variations ~40 per cent, peaking on k ~ 0.1Mpc-1 scales). This induces a distinctive peak-trough structure in the angle-averaged 21-cm power spectrum, which may be accessible to the proposed Square Kilometre Array. This signal reaches the ~10 mK level, and is stronger than that induced by Lyα flux fluctuations. As well as probing the thermal evolution of the IGM before reionization, this 21-cm signal contains information about the spectra of the first X-ray sources. Finally, we consider disentangling temperature, density and Lyα flux fluctuations as functions of redshift.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- April 2007
- DOI:
- 10.1111/j.1365-2966.2007.11519.x
- arXiv:
- arXiv:astro-ph/0607234
- Bibcode:
- 2007MNRAS.376.1680P
- Keywords:
-
- intergalactic medium;
- cosmology: theory;
- diffuse radiation;
- X-rays: diffuse background;
- Astrophysics
- E-Print:
- 14 pages, 12 figures, accepted by MNRAS, subsection and figure added, text reworked for clarity