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

Abstract :
At intermediate to high densities, electron (de-)excitation collisions are the dominant process for populating or depopulating high Rydberg states. In particular, the accurate knowledge of the energy changing (n-changing) collisional rates is determinant for predicting the radio recombination spectra of gaseous nebula. The different datasets present in the literature come either from impact parameter calculations or semi-empirical fits and the rate coefficients agree within a factor of two. We show in this paper that these uncertainties cause errors lower than 5% in the emission of radio recombination lines (RRL) of most ionized plasmas of typical nebulae. However, in special circumstances where the transitions between Rydberg levels are amplified by maser effects, the errors can increase up to 20%. We present simulations of the optical depth and Hnα line emission of Active Galactic Nuclei (AGN) Broad Line Regions (BLRs) and the Orion Nebula Blister to showcase our findings.

Keywords : (ISM:) H II regions; atomic data; atomic processes; masers; radio lines: general; submillimetre: general; Astrophysics - Astrophysics of Galaxies; Physics - Atomic Physics
Publication : Monthly Notices of the Royal Astronomical Society, Advance Access
DOI : 10.1093/mnras/stz857 
Bibcode : 2019MNRAS.tmp..834G