Mathematics – Logic
Scientific paper
Dec 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999sf99.proc...30u&link_type=abstract
Star Formation 1999, Proceedings of Star Formation 1999, held in Nagoya, Japan, June 21 - 25, 1999, Editor: T. Nakamoto, Nobeyam
Mathematics
Logic
Scientific paper
We investigate thermal and dynamical evolutions of a primordial gas cloud whose mass is much higher than the cosmological Jeans mass using an updated deuterium chemistry. Such a cloud collapses to form a shock and fragment. At first we investigate molecule formation in a primordial shock. We show that almost all deuterium can be converted to HD molecule within the age of the universe at the collapsed redshift in case of a cloud which has the virial temperature of 106 K and collapses at z>1. When the postshock cooled sheet fragments due to gravitational instability, the fractional HH and HD abundances become 10-2 and 10-5, respectively, which are 103 - 104 times higher than the results of molecule formation in the expanding universe after recombination. In order to see subsequent evolution of a fragment, we performed one-dimensional simulation of a spherical/cylindrical cloud, of which initial conditions (e.g. fractional abundances of chemical composition, temperature) are derived from results of 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 ç) and gravitational fragmentation of the cylindrical cloud becomes effective, Jeans mass becomes less than 0.1 Modot. This fact suggests the formation of primordial brown dwarfs, which are one of the possible candidates for massive compact halo objects (MACHOs), in primordial gas clouds.
Inutsuka Shu-ichiro
Uehara Hitoshi
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