The H II Region of the First Star

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  • 29 July 2005
Abstract
Numerical simulations predict the first stars in a LCDM universe formed at z>20 in minihalos with masses ~10^6 M_sun. We have simulated 3D propagation of ionization fronts (I-fronts) created by these stars (M_*=15-500 M_sun) that formed in minihalos at z=20, outward thru the minihalo and beyond. We follow the evolving H II region within the gas density field from a cosmological simulation of primordial star formation. The H II region evolves a ``champagne flow,'' once the D-type I-front, preceded by a shock, moves outward down the density gradient inside the minihalo until it detaches from the shock as a weak R-type I-front. A ray-tracing calculation tracks the I-front during this ``champagne phase,'' taking account of the hydrodynamical back-reaction of the gas by an approximate model of the ionized wind. We find that the escape fraction increases with stellar mass, 0.7<f_esc<0.9 for 80<M_*/M_sun 80M_sun, this ratio is ~60,000, roughly half the number of ionizing photons released per stellar baryon during the their lifetimes, independent of stellar mass. In addition, we find that nearby minihalos trap the I-front, so their centers remain neutral. This is contrary to the recent suggestion that these first stars would trigger the formation of a second generation by fully ionizing their neighbor minihalos so as to stimulate molecular hydrogen formation in their cores. Finally, we discuss the effect of evacuating the gas from the host halo on the growth and luminosity of ``miniquasars'' that may form from black holes that are remnants of these stars. (abridged)

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