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arXiv · 2610.32834

The Physics of the Cold and Warm Interstellar Medium Through Radio Recombination Lines

Pedro Salas·Kimberly L. Emig·Matteo Luisi·Antoine Gusdorf·Lucie Cros·Loren D. Anderson·Alexander Tielens
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Abstract

The interplay between star formation and the interstellar medium (ISM) gives rise to a feedback cycle that is one of the key drivers of galaxy evolution. The coldest gas in the ISM provides the fuel for star formation, and, in turn, the ISM is affected by feedback in the form of photons, shocks, and cosmic rays. Radio recombination lines (RRLs) offer a unique way of characterizing the gas in the ISM as extinction free probes of the gas kinematics, density, temperature, and radiation field. Hydrogen RRLs (HRRLs) probe gas where hydrogen is ionized, while carbon RRLs (CRRLs) probe cold gas in the HI-to-H$_{2}$ transition layers. The superb sensitivity, spatial resolution, large field of view, and frequency resolution and coverage of the Square Kilometre Array (SKA) will allow for efficient observations of RRLs, that will make significant impacts to the study of the diffuse ISM. By observing RRLs with the SKA we will be able to determine the thermal and turbulent balance, chemical enrichment, sizes, and ionization rate of the cold and ionized gases from degree-scales down to arcsecond scales in our Galaxy.

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Pedro Salas, Kimberly L. Emig, Matteo Luisi, Antoine Gusdorf, Lucie Cros, Loren D. Anderson, Alexander Tielens. 2026-10-23. The Physics of the Cold and Warm Interstellar Medium Through Radio Recombination Lines. https://arxiv.org/abs/2610.32834

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