Growth of Primeval H2 and HD Inhomogeneities in the Early Universe (original) (raw)
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Possible flakes of molecular hydrogen in the early Universe
Astronomy and Astrophysics, 2003
The thermochemistry of H2 and HD in non-collapsed, non-reionized primordial gas up to the end of the dark age is investigated with recent radiation-matter and chemical reaction rates taking into account the efficient coolant HD, and the possibility of a gas-solid phase transition of H2. In the standard big-bang model we find that these molecules can freeze out and lead to the growth of flakes of solid molecular hydrogen at redshifts z ≈ 6 − 12 in the unperturbed medium and under-dense regions. While this freezing caused by the mere adiabatic cooling of the expanding matter is less likely to occur in collapsed regions due to their higher than radiation background temperature, on the other hand the super-adiabatic expansion in voids strongly favors it. Later reionization (at z ≈ 5 − 6) eventually destroys all these H2 flakes. The possible occurrence of H2 flakes is important for the degree of coupling between matter and radiation, as well as for the existence of a gas-grain chemistry at the end of the dark age.
Molecular Hydrogen in Space: Evolution of Primordial H2 for Different Cosmological Models
2000
Primordial chemistry began in the recombination epoch when the adiabatic expansion caused the temperature of the radiation to fall below 4000 K. The chemistry of the early Universe involves the elements hydrogen, its isotope deuterium, helium with its isotopic forms and lithium. In this talk I will present results on the evolution of the primordial H2 abundance for different cosmological models and the influence on the thermal decoupling.
Molecules in the early universe
The Astrophysical Journal, 1984
We study the formation of first molecules, negative Hydrogen ions and molecular ions in model of the Universe with cosmological constant and cold dark matter. The cosmological recombination is described in the framework of modified model of the effective 3-level atom, while the kinetics of chemical reactions in the framework of the minimal model for Hydrogen, Deuterium and Helium. It is found that the uncertainties of molecular abundances caused by the inaccuracies of computation of cosmological recombination are about 2-3%. The uncertainties of values of cosmological parameters affect the abundances of molecules, negative Hydrogen ions and molecular ions at the level of up to 2%. In the absence of cosmological reionization at redshift z = 10 the ratios of abundances to the Hydrogen one are 3.08×10 −13 for H − , 2.37×10 −6 for H 2 , 1.26×10 −13 for H + 2 , 1.12×10 −9 for HD and 8.54 × 10 −14 for HeH + .
HD/H 2 molecular clouds in the early Universe: The problem of primordial deuterium
Astronomy Letters-a Journal of Astronomy and Space Astrophysics, 2010
We have detected new HD absorption systems at high redshifts, z abs = 2.626 and z abs = 1.777, identified in the spectra of the quasars J0812+3208 and Q1331+170, respectively. Each of these systems consists of two subsystems. The HD column densities have been determined: log N HDA = 15.70 ± 0.07 for z A = 2.626443(2) and log N HDB = 12.98 ± 0.22 for z B = 2.626276(2) in the spectrum of J0812+3208 and log N HDC = 14.83 ± 0.15 for z C = 1.77637(2) and log N HDD = 14.61 ± 0.20 for z D = 1.77670(3) in the spectrum of Q1331+170. The measured HD/H2 ratio for three of these subsystems has been found to be considerably higher than its values typical of clouds in our Galaxy.We discuss the problem of determining the primordial deuterium abundance, which is most sensitive to the baryon density of the Universe Ωb. Using a well-known model for the chemistry of a molecular cloud, we have estimated the isotopic ratio D/H=HD/2H2 = (2.97 ± 0.55) × 10−5 and the corresponding baryon density Ωbh 2 = 0.0205 −0.0020+0.0025. This value is in good agreement with Ωbh 2 = 0.0226 −0.00060.0006 obtained by analyzing the cosmic microwave background radiation anisotropy. However, in high-redshift clouds, under conditions of low metallicity and low dust content, hydrogen may be incompletely molecularized even in the case of self-shielding. In this situation, the HD/2H2 ratio may not correspond to the actual D/H isotopic ratio. We have estimated the cloud molecularization dynamics and the influence of cosmological evolutionary effects on it.
The Astrophysical Journal Supplement Series, 2012
Energy exchange processes play a crucial role in the early Universe, affecting the thermal balance and the dynamical evolution of the primordial gas. In the present work we focus on the consequences of a non-thermal distribution of the level populations of H 2 : first, we determine the excitation temperatures of vibrational transitions and the non-equilibrium heat transfer; second, we compare the modifications to chemical reaction rate coefficients with respect to the values obtained assuming local thermodynamic equilibrium; third, we compute the spectral distortions to the cosmic background radiation generated by the formation of H 2 in vibrationally excited levels. We conclude that non-equilibrium processes cannot be ignored in cosmological simulations of the evolution of baryons, although their observational signatures remain below current limits of detection. New fits to the equilibrium and non-equilibrium heat transfer functions are provided.
Deuterated hydrogen molecule and search for early structure-formation signatures in the Universe
Monthly Notices of the Royal Astronomical Society, 2006
Possible detection of signatures of structure formation at the end of the 'dark age' epoch (z ∼ 40 − 20) is examined. We discuss the spectral-spatial fluctuations in the CMBR temperature produced by elastic resonant scattering of CMBR photons on HD molecules located in protostructures moving with peculiar velocity. Detailed chemical kinematic evolution of HD molecules in the expanding homogeneous medium is calculated. Then, the HD abundances are linked to protostructures at their maximum expansion, whose properties are estimated by using the top-hat spherical approach and the ΛCDM cosmology. We find that the optical depths in the HD three lowest pure rotational lines for high-peak protohaloes at their maximum expansion are much higher than those in LiH molecule. The corresponding spectralspatial fluctuation amplitudes however are probably too weak as to be detected by current and forthcoming millimeter-telescope facilities. We extend our estimates of spectral-spatial fluctuations to gas clouds inside collapsed CDM haloes by using results from a crude model of HD production in these clouds. The fluctuations for the highest-peak CDM haloes at redshifts ∼ 20 − 30 could be detected in the future. Observations will be important to test model predictions of early structure formation in the universe.
Insights Into Chemical Reactions at the Beginning of the Universe: From HeH+ to H3 +
Frontiers in Chemistry, 2021
At the dawn of the Universe, the ions of the light elements produced in the Big Bang nucleosynthesis recombined with each other. In our present study, we have tried to mimic the conditions in the early Universe to show how the recombination process would have led to the formation of the first ever formed diatomic species of the Universe: HeH+, as well as the subsequent processes that would have led to the formation of the simplest triatomic species: H3 +. We have also studied some special cases: higher positive charge with fewer number of hydrogen atoms in a dense atmosphere, and the formation of unusual and interesting linear, dicationic He chains beginning from light elements He and H in a positively charged atmosphere. For all the simulations, the ab initio nanoreactor (AINR) dynamics method has been employed.