Did the universe recombine? New spectral constraints on reheating
Abstract
One still cannot conclusively assert that the universe underwent a neutral phase, despite the new COBE FIRAS limit y<0.000025 on Compton y-distortions of the cosmic microwave background. Although scenarios where the very early (z=1000) ionization is thermal, caused by IGM temperatures exceeding 10000K, are clearly ruled out, there is a significant loophole for cosmologies with typical CDM parameters if the dominant ionization mechanism is photoionization. If the ionizing radiation has a typical quasar spectrum, then the y-constraint implies roughly h^{3/2}\Omega_b Omega_0^{-1/4}<0.1 for fully ionized models. This means that BDM models with Omega_0 around 0.15 and reionization at about z=1000 are strongly constrained even in this very conservative case, and can survive the y test only if most of the baryons form BDM around the reionization epoch.
Cite
@article{arxiv.astro-ph/9307018,
title = {Did the universe recombine? New spectral constraints on reheating},
author = {Max Tegmark and Joseph Silk},
journal= {arXiv preprint arXiv:astro-ph/9307018},
year = {2009}
}
Comments
15 pages, incl 3 figures. Stone-age postscript replaced by LATeX. Latest version at http://www.sns.ias.edu/~max/y.html (faster from the US), from http://www.mpa-garching.mpg.de/~max/y.html (faster from Europe) or from [email protected]