Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001mnras.328..969b&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Volume 328, Issue 3, pp. 969-976.
Astronomy and Astrophysics
Astronomy
218
Hydrodynamics, Stars: Formation, Galaxies: Formation, Cosmology: Theory, Early Universe
Scientific paper
Recent theoretical investigations have suggested that the formation of the very first stars, forming out of metal-free gas, was fundamentally different from the present-day case. The question then arises which effect was responsible for this transition in the star formation properties. In this paper, we study the effect of metallicity on the evolution of the gas in a collapsing dark matter mini-halo. We model such a system as an isolated 3σ peak of mass 2×106Msolar that collapses at zcoll~=30, using smoothed particle hydrodynamics. The gas has a supposed level of pre-enrichment of either Z=10-4Zsolar or 10-3Zsolar. We assume that H2 has been radiatively destroyed by the presence of a soft UV background. Metals therefore provide the only viable cooling at temperatures below 104K. We find that the evolution proceeds very differently for the two cases. The gas in the lower metallicity simulation fails to undergo continued collapse and fragmentation, whereas the gas in the higher metallicity case dissipatively settles into the centre of the dark matter halo. The central gas, characterized by densities nH>~104cm-3, and a temperature, T~=90K, that closely follows that of the cosmic microwave background, is gravitationally unstable and undergoes vigorous fragmentation. We discuss the physical reason for the existence of a critical metallicity, Zcrit~5×10-4Zsolar, and its possible dependence on redshift. Compared with the pure H/He case, the fragmentation of the Z=10-3Zsolar gas leads to a larger relative number of low-mass clumps.
Bromm Volker
Coppi Paolo S.
Ferrara Andrea
Larson Richard B.
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