Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010dmap.conf..350p&link_type=abstract
DARK MATTER IN ASTROPHYSICS AND PARTICLE PHYSICS . Proceedings of the 7th International Heidelberg Conference on Dark 2009 . Hel
Astronomy and Astrophysics
Astrophysics
Scientific paper
The primordial molecules, which appear during the phase of cosmological recombination, play an important role in the mechanisms of formation of the first gravitational structures. Their thermal influence on the gravitational dynamics of collapse can generate, under certain conditions, an instability which leads to the fragmentation of the initial collapsing structure. In this framework it is crucial to establish the initial conditions of the mechanism of gravitational collapse, in particular the abundances of molecules susceptible to have a thermal influence as the primordial molecules.
In a Universe made of baryonic and non-baryonic dark matter, we need to discuss how each component couples with the other, and how this coupling may modify the primordial chemistry during the gravitational growth of structures. Since dark matter is assumed to be affected only by gravity and is collisionless, there is no effective pressure term in its equation of evolution. The linearized continuity equation in Fourier modes describes the dark matter and baryon fluids by two second-order differential equations which couple the baryon chemistry and gas dynamics to dark-matter by gravity.
In this contribution besides to remind the chemical processes in the early Universe, we shall analyze the influence that these last ones can have on the formation of the first baryonic structures gravitational. Thus, we present calculations in the linear approximation of density fluctuations, but in the full non-linear regime of chemical abundances about the primordial molecule formation in a uniform medium perturbed by small density inhomogeneities at various spatial wavelengths. We analyze the differential abundances of the primordial molecules H2, HD and LiH. As the Universe expands, the baryonic fluctuations increase and induce strong contrasts on the primordial molecular abundances.
The main result is that the chemical abundances at the transition between the linear and non-linear regimes of density fluctuations (such as in proto-collapsing structures) are already very inhomogeneous and scale dependent. These results indicate that pronounced inhomogeneous chemical abundances are present already before and during the dark age. This must have a direct consequence on the mass spectrum of the first bound objects since gas cooling depends then mainly on the particular abundances of H2 and HD.
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