HD/H2 Molecular Clouds in the Early Universe: The Problem of Primordial Deuterium

Abstract

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(HD),A)=15.70+/-0.07 for z_A=2.626443(2) and log(N(HD),B)=12.98+/-0.22 for z_B=2.626276(2) in the spectrum of J0812+3208 and log(N(HD),C)=14.83+/-0.15 for z_C=1.77637(2) and log(N(HD),D)=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 Ω_{b}. Using a well-known model for the chemistry of a molecular cloud, we have estimated the isotopic ratio D/H=HD/2H_2=(2.97+/-0.55)x10^{-5} and the corresponding baryon density Ω_{b}h^2=0.0205^{+0.0025}_{-0.0020}. This value is in good agreement with Ω_{b}h^2=0.0226^{+0.0006}_{-0.0006} 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/2H_2 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.

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• Search for a drifting proton--electron mass ratio from H${}_2$
• Higher D or Li: Probes of Physics beyond the Standard Model
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• Spotting high-z molecular absorbers using neutral carbon: Results from a complete spectroscopic survey with the VLT
• Deuterium at high-redshift: Primordial abundance in the zabs = 2.621 damped Ly-alpha system towards CTQ247
• HD/H2 as a probe of the roles of gas, dust, light, metallicity and cosmic rays in promoting the growth of molecular hydrogen in the diffuse interstellar medium
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• Partial covering of emission regions of Q 0528-250 by intervening H${}_2$ clouds
• Estimation of the CMB temperature from atomic C\,{\sc i} and molecular CO lines in the interstellar medium of early galaxies
• Physical conditions in diffuse interstellar medium of local and high redshift galaxies: measurements based on excitation of H${}_2$ rotational and CI fine-structure levels
• Multicomponent H2 in DLA at zabs = 2.05: physical conditions through observations and numerical models
• HD molecules at high redshift: cosmic-ray ionization rate in the diffuse interstellar medium
• HD/H${}_2$ ratio in the diffuse interstellar medium
• H${}_2$/HD molecular data for analysis of quasar spectra in search of varying constants
• Estimation of physical conditions in the cold phase of the ISM in the sub-DLA system at z = 2.06 in the spectrum of the quasar J2123-0050
• Nature of the DLA towards Q0528-250: High pressure and strong UV field revealed by excitation of CI, H2 and SiII
• Gas and Star Formation from HD and Dust Emission in a Strongly Lensed Galaxy
• Search for cosmological mu variation from high redshift H2 absorption; a status report
• Extremely strong DLAs at high redshift: Gas cooling and H${}_2$ formation
• Neutral carbon in diffuse interstellar medium: abundance matching with H2 for DLAs at high redshifts
• Effects of active-sterile neutrino mixing during primordial nucleosynthesis
• Molecular hydrogen in absorption at high redshifts. Science cases for CUBES
• Calculation of primordial abundances of light nuclei including a heavy sterile neutrino
• Lorentzian correction for the evolution of the CMB temperature
• Influence of radiative pumping on the HD rotational level populations in diffuse molecular clouds of the interstellar medium