Wednesday, October 11, 2006 - 3:15pm
Dr. Anne-Katharina Jappsen (CITA):
"Influence of Metallicity on Fragmentation of Protogalactic Gas"
Abstract. 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 protogalaxies 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. We use 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 per cent 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 and 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.