Astronomy Colloquium / Fall 2006

October 18

Dr. Brian O'Shea

Los Alamos National Laboratory

Population III stars and the formation of the first protogalaxies

I use the cosmological adaptive mesh refinement code Enzo to do a suite of high-resolution numerical simulations of Population III protostellar clouds in a cosmological context. These calculations examine the formation of primordial protostellar clouds at a range of redshifts and in differing cosmic "neighborhoods." I find that these cores have a wide variety of accretion rates - varying by over two orders of magnitude - which may have significant implications for the IMF of Population III stars. I then simulate supernovae from the inferred stellar mass range and follow the evolution of the ensuing supernova remnant until the deposition of metal-enriched gas in the next generation of halos, which generally occurs ~50 million years after the original supernova. The dense gas in the core of these "child" halos is typically enriched to metallicities of ~10^-3 solar, which is above the "critical metallicity" at which metal line cooling dominates over molecular cooling, and suggests that the stars in these halos will have a significantly lower mass range than their Population III parents. This metal enrichment is a local phenomenon, and the transition of the universe from primordial to metal-enriched gas will be quite extended.