Mathematics – Logic
Scientific paper
Aug 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006iaujd...7e..24j&link_type=abstract
The Universe at z > 6, 26th meeting of the IAU, Joint Discussion 7, 17-18 August 2006, Prague, Czech Republic, JD07, #24
Mathematics
Logic
Scientific paper
In cold dark matter cosmological models, the first stars to form are believed to do so within small protogalaxies. We wish to understand how the evolution of these early proto-galaxies changes once the gas forming them has been enriched with small quantities of heavy elements, which are produced and dispersed into the intergalactic medium by the first supernovae. Adding heavy elements to the gas, whether in the form of individual atoms or as microscopic dust grains, increases its ability to radiate heat and to control its temperature. It has been argued that enrichment beyond a certain "critical metallicity" that allows the first solar-mass stars to form, while proto-galaxies with fewer metals form only massive stars, with masses greater than a hundred times solar. This idea has been accepted as a working hypothesis by many cosmologists, but it has yet to be rigorously tested. Although observational tests will not be feasible until the next generation of telescopes become available, we can begin to test this idea numerically, using high-resolution hydrodynamic simulations that incorporate the effects of the appropriate chemical and thermal processes. Our initial conditions represent protogalaxies forming within a fossil HII region - a previously ionized region that has not yet had time to cool and recombine. We study the influence of low levels of metal enrichment on the cooling and collapse of ionized gas in small protogalactic halos using three-dimensional, smoothed particle hydrodynamics simulations. Our preliminary simulations demonstrate that for metallicities Z ≤ 10^-3 Z[Sun], metal line cooling alters the density and temperature evolution of the gas by less than 1% compared to the metal-free case at densities below 1 cm^-3 and temperatures above 2000 K (Jappsen et al. 2006). We also present the results of high-resolution simulations using particle splitting (Kitsionas & Whitworth 2002) to improve resolution in regions of interest. These simulations allow us to address the question of whether or not there is a critical metallicity above which fine structure cooling from metals that allows efficient fragmentation to occur, producing a modern IMF rather than only high-mass stars.
Glover Simon C. O.
Jappsen Anne-Katharina
Kitsionas Spyridon
Klessen Ralf S.
Mac Low Mordecai-Mar
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