Astronomy and Astrophysics – Astronomy
Scientific paper
May 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993aas...182.1302m&link_type=abstract
American Astronomical Society, 182nd AAS Meeting, #13.02; Bulletin of the American Astronomical Society, Vol. 25, p.813
Astronomy and Astrophysics
Astronomy
Scientific paper
We examine the Hogan-Rees photoionization instability (Hogan 1992, Nature 359, 40) in the context of an Omega =1 universe dominated by massive (m_nu ~ 30 eV) decaying neutrinos. In a medium with a smoothly distributed source of ionizing radiation, the photoionization and heating rates on scales larger than the photon mean free path are independent of the local gas density. Thus, underdense regions receive more energy per particle and heat up faster; this nonadiabatic temperature change produces a pressure term which drives the growth of fluctuations. Hogan (1992) showed that in a static medium this instability produces exponential growth, with growth rates which can be much larger than the expansion rate in the expanding universe. We have found that on small scales (comoving wavenumber k > k_m, where k_m corresponds to lambda ~ 10(-2) Mpc present-day), the growth remains exponential in an expanding universe. The instability growth rate is independent of scale for k > k_m, and declines rapidly with increasing scale, so the characteristic mass produced by the instability will correspond to k ~ k_m. For a neutrino energy above the Lyman limit Delta E (~ m_nu /2-13.6 eV) of a few eV and a decay lifetime T ~ 10(24) seconds, fluctuations at the Poisson level on the scale k_m can grow to non-linearity between z ~ 70 (when Compton cooling inhibits the instability) and z ~ 20 (when the intergalactic medium becomes ionized).
Giroux Mark
Maloney Philip
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