Halos in Dark Ages: formation and chemistry

Abstract

Formation of halos in the Dark Ages from initial spherical perturbations is analyzed in a four component Universe (dark matter, dark energy, baryonic matter and radiation) in the approximation of relativistic hydrodynamics. Evolution of density and velocity perturbations of each component is obtained by integration of a system of nine differential equations from $z=10^8$ up to virialization, which is described phenomenologically. It is shown that the number density of dark matter halos with masses $M\sim 10^8-10^9{\mathrm{M}}_{\odot }$ virialized at $z\sim 10$ is close to the number density of galaxies in comoving coordinates. The dynamical dark energy of classical scalar field type does not significantly influence the evolution of the other components, but dark energy with a small value of effective sound speed can affect the final halo state. Simultaneously, the formation/dissociation of the first molecules have been analyzed in the halos which are forming. The results show that number densities of molecules ${\mathrm{H}}_2$ and $\mathrm{HD}$ at the moment of halo virialization are $\sim 10^3$ and $\sim 400$ times larger, respectively, than on a uniformly expanding background. It is caused by increased density and rates of reactions at quasilinear and nonlinear evolution stages of density and velocity of the baryonic component of halos. It is shown also that the temperature history of the halo is important for calculating the concentration of molecular ions with low binding energy. So, in a halo with virial temperature $\sim 10^5$ K the number density of the molecular ion HeH${}^{+}$ is approximately 100 times smaller than that on the cosmological background.

arXiv comment10 pages, 4 figures, 2 tables; accepted for publication in The Astrophysical Journal

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Cited by in corpus (6)

• The first molecules in the intergalactic medium and halos of the Dark Ages and Cosmic Dawn
• Thermal and Resonant Emission of Dark Ages Halos in the Rotational Lines of HeH${}^{+}$
• Hydrogen Molecules in the Dark Ages Halos: Thermal Emission vs. Resonant Scattering
• Redshifted 21-cm emission signal from the halos in Dark Ages
• Distortion of the CMB spectrum by the first molecules of the Dark Ages
• Global Signals of the First Molecules from the Dark Ages in the Presence of Primordial Magnetic Fields