4.4 Lyman-alpha Forest4 PHYSICAL COSMOLOGY4.2 Gravitational Lensing

4.3 First Star Formation 

In CDM cosmogonies, the fluctuation spectrum at small wavelengths has a logarithmic dependence at mass scales smaller than image solar masses, which indicates that all small scale fluctuations in this model collapse nearly simultaneously in time. This leads to very complex dynamics during the formation of these first structures. Furthermore, the cooling in these fluctuations is dominated by the rotational/vibrational modes of hydrogen molecules that were able to form using the free electrons left over from recombination and the ones produced by strong shock waves as catalysts. The first structures to collapse may be capable of producing population III stars and have a substantial influence on the subsequent thermal evolution of the intergalactic medium, as suggested by Figure 1, due to the radiation emitted by the first generation stars as well as supernova driven winds. To know the subsequent fate of the Universe and which structures will survive or be destroyed by the UV background, it is first necessary to know when the first stars formed.

Ostriker and Gnedin [46] have carried out high resolution numerical simulations of the reheating and reionization of the Universe due to star formation bursts triggered by molecular hydrogen cooling. Accounting for the chemistry of the primeval hydrogen/helium plasma, self-shielding of the gas, radiative cooling, and a phenomenological model of star formation, they find that two distinct star populations form: the first generation pop III from image cooling prior to reheating at redshift image ; and the second generation pop II at z <10 when the virial temperature of the gas clumps reaches image K and hydrogen line cooling becomes efficient. Star formation slows in the intermittent epoch due to the depletion of image by photo-destruction and reheating. In addition, the objects which formed pop III stars also initiate pop II sequences when their virial temperatures reach image K through continued mass accretion.



4.4 Lyman-alpha Forest4 PHYSICAL COSMOLOGY4.2 Gravitational Lensing

image Computational Cosmology: from the Early Universe to the Large Scale Structure
Peter Anninos
http://www.livingreviews.org/lrr-1998-9
© Max-Planck-Gesellschaft. ISSN 1433-8351
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