Inverted level populations of hydrogen atoms in ionized gas

Abstract

Context. Level population inversion of hydrogen atoms in ionized gas may lead to stimulated emission of hydrogen recombination lines, and the level populations can in turn be affected by powerful stimulated emissions. Aims. In this work the interaction of the radiation fields and the level population inversion of hydrogen atoms is studied. The effect of the stimulated emissions on the line profiles is also investigated. Methods. Our previous nl-model for calculating level populations of hydrogen atoms and hydrogen recombination lines is improved. The effects of line and continuum radiation fields on the level populations are considered in the improved model. By using this method the properties of simulated hydrogen recombination lines and level populations are used in analyses. Results. The simulations show that hydrogen radio recombination lines are often emitted from the energy level with an inverted population. The widths of Hn$\alpha$ lines can be significantly narrowed by strong stimulated emissions to be even less than 10 km s${}^{-1}$. The amplification of hydrogen recombination lines is more affected by the line optical depth than by the total optical depth. The influence of stimulated emission on the estimates of electron temperature and density of ionized gas is evaluated. We find that comparing multiple line-to-continuum ratios is a reliable method for estimating the electron temperature, while the effectiveness of the estimation of electron density is determined by the relative significance of stimulated emission.

Accepted for published in A&A. 25 pages, 13 figures

References in corpus (10)

• The Early Evolution of Massive Stars: Radio Recombination Line Spectra
• ATOMS:ALMA Three-millimeter Observations of Massive Star-forming regions -- III :Catalogues of candidate hot molecular cores and Hyper/Ultra compact HII regions
• Understanding hydrogen recombination line observations with ALMA and EVLA
• Low Frequency Carbon Radio Recombination Lines I: Calculations of Departure Coefficients
• Large-scale Map of Millimeter-wavelength Hydrogen Radio Recombination Lines around a Young Massive Star Cluster
• Ultracompact H II Regions with Extended Emission: The Complete View
• H-, He-like recombination spectra III: $n$-changing collisions in highly-excited Rydberg states and their impact on the radio, IR and optical recombination lines
• A 4-6 GHz Radio Recombination Line Survey in the Milky Way
• Determining electron temperature and density in a H II region by using the relative strengths of hydrogen radio recombination lines
• Ultracompact HII regions with extended emission: The case of G43.89-0.78 and its molecular environment

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• An nl-model with a full radiative transfer treatment for level populations of hydrogen atoms in a spherically symmetric H II region