An Instability in the Radiative Ionization of Atomic Hydrogen/Helium Gas
Abstract
We show that the process of photoionizing a gas of atomic hydrogen and helium by line radiation whose energy is slightly above the helium single-ionization threshold is unstable if the helium fraction by number is less than approximately one-half. However, in the two scenarios we consider here, based on the decaying dark matter (DDM) model of cosmological reionization, there is no significant growth. In the first scenario, we consider ionization and recombination to be approximately in equilibrium. This is relevant to high photon flux rates and early reionization, but in that case the heating is balanced by Compton cooling, which is very stabilizing. In the second scenario, we ignore recombination. This is relevant to low photon flux rates, or to the last stage of the reionization. In that case, there is too little growth on a cosmological timescale to be significant.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- October 1996
- DOI:
- 10.1086/177856
- arXiv:
- arXiv:astro-ph/9604075
- Bibcode:
- 1996ApJ...470..149B
- Keywords:
-
- ATOMIC PROCESSES;
- COSMOLOGY: THEORY;
- COSMOLOGY: DARK MATTER;
- COSMOLOGY: EARLY UNIVERSE;
- INSTABILITIES;
- COSMOLOGY: LARGE-SCALE STRUCTURE OF UNIVERSE;
- Astrophysics
- E-Print:
- 23 pages, AASTeX. Five postscript figures included. To appear in the Astrophysical Journal. Uses the Astrobib style for BibTeX