Presentation #343.12 in the session Potpourri of Galaxies — iPoster Session.
We aim to understand the structure of the interstellar medium (ISM) of M82, a nearby starburst galaxy of a distance 3.6 Mpc, through radio recombination line (RRL) observations of the ionized gas in the central starburst region of the galaxy. We present a model of the ionized gas from measurements of the RRL emission of hydrogen. We utilize 8 measurements of the hydrogen RRL emission with frequencies ranging from 1.4 GHz to 316 GHz. We plot the RRL emission against frequency and trace a line of best fit with a power-law slope of 1.07 ± 0.20 to the higher frequency (>30 GHz) data points. The slope indicates that the line emission is a result of spontaneous electron transitions, and it directly reflects the ionizing photon rate. We focus on the lower frequency points to further investigate the composition of the center region containing ionized gas. Geometrical assumptions of the ISM are formed to derive a pathlength, density, and emission measure of the ionized gas in the region and to reproduce models of the RRL emission. We find one set of physical conditions that outlines the general behavior of the measurements but is unable to explain the entirety of the observed line flux densities. To construct a more robust characterization of the line emission from M82, the next step of this project will be to include a model of a collection of HII regions (i.e., young, massive clusters) and synchrotron radiation at lower frequencies.