Directional Radiation and Photodissociation Regions in Molecular Hydrogen Clouds

Abstract

Some astrophysical observations of molecular hydrogen point to a broadening of the velocity distribution for molecules at excited rotational levels. This effect is observed in both Galactic and high redshift clouds. Analysis of H_2, HD, and CI absorption lines has revealed the broadening effect in the absorption system of QSO 1232+082 (z_{abs}=2.33771). We analyze line broadening mechanisms by considering in detail the transfer of ultraviolet radiation (in the resonance lines of the Lyman and Werner H_2 molecular bands) for various velocity distributions at excited rotational levels. The mechanism we suggest includes the saturation of the lines that populate excited rotational levels (radiative pumping) and manifests itself most clearly in the case of directional radiation in the medium. Based on the calculated structure of a molecular hydrogen cloud in rotational level populations, we have considered an additional mechanism that takes into account the presence of a photodissociation region. Note that disregarding the broadening effects we investigated can lead to a significant systematic error when the data are processed.

14 pages, 10 figures

References in corpus (2)

• Molecular hydrogen in high-redshift Damped Lyman-alpha systems: The VLT/UVES database
• Excitation mechanisms in newly discovered H2-bearing Damped Lyman-alpha clouds: systems with low molecular fractions

Cited by in corpus (13)

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• HD/H2 Molecular Clouds in the Early Universe: The Problem of Primordial Deuterium
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• HD molecules at high redshift: The absorption system at z=2.3377 towards Q 1232+082
• Observational Properties of Rotationally Excited Molecular Hydrogen In Translucent Lines of Sight
• Constraint on a varying proton-to-electron mass ratio from H2 and HD absorption at z = 2.34
• 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
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• Down-the-barrel observations of a multiphase quasar outflow at high redshift: VLT/X-shooter spectroscopy of the proximate molecular absorber at z=2.631 towards SDSS J001514+184212
• Proximate molecular quasar absorbers: Chemical enrichment and kinematics of the neutral gas
• A detection of H${}_2$ in a high velocity cloud toward the Large Magellanic Cloud
• Quasar radiation transforms the gas in a merging companion galaxy