Computer Science
Scientific paper
Sep 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001phdt.........6s&link_type=abstract
Thesis (PhD). MICHIGAN STATE UNIVERSITY, Source DAI-B 62/03, p. 1433, Sep 2001, 122 pages.
Computer Science
1
Scientific paper
We perform a numerical simulation to describe the evolution of pre-Galactic clouds in a manner similar to that suggested by the cold dark matter scenario of hierarchical galaxy formation, and adopting a SN-induced star-formation mechanism. The model includes chemical enrichment of the clouds by SN of type II and type Ia, and their associated energy input. It utilizes metallicity-dependent yields for all elements at all times, and takes into consideration the lifetimes of stars. The model calculates the metallicity distribution functions for stars in the clouds, their age-metallicity relation, and relative elemental abundances for several alpha- and Fe-group elements. The stability of these clouds against destruction is discussed, and results are compared for different initial mass functions. We find that the dispersion of the metallicity distribution function observed in the outer halo is reproduced by evolving many clouds with different initial conditions. The scatter in metallicity as a function of age for these stars is very large, implying that no age- clouds are only stable when one assumes an initial mass function that is not biased towards massive stars, indicating that even if the first stars were formed according to a top-heavy mass function, subsequent star formation was likely to have proceeded with a present-day mass function, or happened in an episodic manner. The predicted relative abundances of alpha- and Fe-group elements compared to iron show good agreement with the observed values down to a metallicity [Fe/H] = -4. The observed scatter is reproduced fairly well for most elements but the model shows larger deviations for some elements. The contributions to the abundances from SN with different progenitor masses and metallicity are discussed. The results suggest that the low-mass end of SN of type-II was probably absent at the very lowest metallicities, and that the high-mass limit for the first stars that contributed to nucleosynthesis may be less than 40 Msolar .
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