Detection of Voigt Spectral Line Profiles of Hydrogen Radio Recombination Lines toward Sagittarius B2(N)

TL;DR

This study reports the detection of Voigt profiles in hydrogen radio recombination lines toward Sagittarius B2(N), confirming pressure broadening effects at high principal quantum numbers using the Green Bank Telescope.

Contribution

First detection of Voigt spectral line profiles in RRLs toward Sagittarius B2(N), demonstrating pressure broadening effects at high quantum numbers with high-sensitivity GBT observations.

Findings

RRLs with n>90 deviate from Gaussian profiles

Voigt profiles accurately describe high-n RRLs

GBT's capabilities enable detailed RRL profiling

Abstract

We report the detection of Voigt spectral line profiles of radio recombination lines (RRLs) toward Sagittarius B2(N) with the 100-m Green Bank Telescope (GBT). At radio wavelengths, astronomical spectra are highly populated with RRLs, which serve as ideal probes of the physical conditions in molecular cloud complexes. An analysis of the Hn(alpha) lines presented herein shows that RRLs of higher principal quantum number (n>90) are generally divergent from their expected Gaussian profiles and, moreover, are well described by their respective Voigt profiles. This is in agreement with the theory that spectral lines experience pressure broadening as a result of electron collisions at lower radio frequencies. Given the inherent technical difficulties regarding the detection and profiling of true RRL wing spans and shapes, it is crucial that the observing instrumentation produce flat baselines as well as high sensitivity, high resolution data. The GBT has demonstrated its capabilities regarding all of these aspects, and we believe that future observations of RRL emission via the GBT will be crucial towards advancing our knowledge of the larger-scale extended structures of ionized gas in the interstellar medium (ISM).