Astronomy and Astrophysics – Astronomy
Scientific paper
Mar 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000apj...531l..91u&link_type=abstract
The Astrophysical Journal, Volume 531, Issue 2, pp. L91-L94.
Astronomy and Astrophysics
Astronomy
74
Cosmology: Theory, Hydrodynamics, Molecular Processes, Stars: Formation
Scientific paper
We investigate thermal and dynamical evolution of a primordial gas cloud with an updated deuterium chemistry. We consider a fragment of a postshock-cooled sheet that is expected to form by collapse of a massive cloud (>~108 Msolar) and by blast waves due to supernova explosions. At first we investigate molecule formation in a primordial shock. We show that almost all deuterium can be converted to HD within the age of the universe at the collapsed redshift in the case of a cloud that has a virial temperature of ~106 K and collapses at z>1. When the postshock sheet fragments owing to gravitational instability, the fractional H2 and HD abundances become ~10-2 and ~10-5, respectively, which are 103-104 times higher than the result of molecule formation in the expanding universe after recombination. To study the subsequent evolution of a fragment, we performed one-dimensional simulations of a spherical/cylindrical cloud, of which initial conditions (e.g., fractional abundances of chemical composition, temperature) are derived from the result of the shock. It is found that, in case of a cylindrical collapse, the cooling by HD molecules keeps the temperature of the cloud less than 100 K and the cloud evolves almost isothermally. When the cloud becomes optically thick to the HD line emission (~1010 cm-3) and the gravitational fragmentation of the cylindrical cloud becomes effective, the Jeans mass becomes comparable to 0.1 Msolar. This series of processes enables the formation of primordial low-mass stars, and possibly brown dwarfs, in primordial gas clouds.
Inutsuka Shu-ichiro
Uehara Hideya
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