The influence of continuum radiation fields on hydrogen radio recombination lines

TL;DR

This paper models how external radiation fields affect hydrogen radio recombination lines, revealing up to 20% differences from previous results and providing new tables for interpreting observations.

Contribution

It introduces a novel numerical approach with improved convergence for calculating hydrogen departure coefficients considering external radiation fields.

Findings

External radiation fields significantly influence hydrogen level populations.

New numerical techniques improve the accuracy and efficiency of modeling.

Tables of emission and absorption coefficients are provided for observational analysis.

Abstract

Calculations of hydrogen departure coefficients using a model with the angular momentum quantum levels resolved that includes the effects of external radiation fields are presented. The stimulating processes are important at radio frequencies and can influence level populations. New numerical techniques with a solid mathematical basis have been incorporated into the model to ensure convergence of the solution. Our results differ from previous results by up to 20 per cent. A direct solver with a similar accuracy but more efficient than the iterative method is used to evaluate the influence of continuum radiation on the hydrogen population structure. The effects on departure coefficients of continuum radiation from dust, the cosmic microwave background, the stellar ionising radiation, and free-free radiation are quantified. Tables of emission and absorption coefficients for interpreting observed radio recombination lines are provided.