Stars constantly inject energy in the interstellar medium of their parent galaxy, in the form of kinetic energy (shocks and turbulence), photons (mostly ultraviolet, but also X- and -rays), and cosmic rays. All these energetic injection mechanisms play a crucial role on the future generations of star formation, and a key role on the energetic balance of galaxies, as well as on the cycle of matter (the so-called astrochemistry) of galaxies.
Being able to model the evolution of galaxies requires understanding the evolution of the interstellar medium, which includes quantifying all the possible effects of feedback of stars on their parent galaxy. Doing so requires the measure of physical and chemical state of the gas in the regions where stars interact with the interstellar medium.
Among the quantities that are important to understand and characterize the impacts of shocks, energetic photons and cosmic rays are the electron density and the magnetic field. With this proposal, we aim at constraining the electron density from the observation of radio recombination lines of carbon and hydrogen.
Our longer-term aim is to combine our results with Faraday tomography in order to constrain also the magnetic field, in regions where the feedback of stars on the interstellar medium is proeminent. Given the various observational uncertainties, our program will be a pilot program at first, but we are keen on making it evolve towards a Key Program when the feasibility of our studies is demonstrated.