Ubiquitous spectral complexity in the atomic ISM across the Local Group

Eric Koch

Thursday December 3rd, 15:15

Encoded in the atomic ISM is physics crucial to the baryonic cycle, including the formation of molecular clouds and the origin of interstellar turbulence from stellar feedback. Nearby galaxies provide an important top-down view on how these processes act over a wide range of ISM environments, however, existing extragalactic observations of the 21-cm HI line have limited resolution---both spatial and spectral---that provides a coarse view of the intricate atomic gas structure that has long been studied within the Milky Way. To bridge our Galactic and extragalactic views of the atomic ISM, I present the initial results from a new 21-cm HI VLA survey of M31 and M33 on 80 pc scales. These new observations combine high sensitivity with fine spectral resolution to reveal ubiquitous HI spectral complexity. In this talk, I will show that the HI spectra strongly prefer a multi-component Gaussian model over an opacity-corrected single component model, in contrast to previous HI studies of nearby galaxies. From this modelling, I will show our first results from decomposing this spectral complexity to trace the location of cool atomic gas and its relation to molecular clouds. By mapping these environmental variations, the product of this decomposition will provide a crucial galaxy-scale perspective for Milky Way studies of molecular cloud formation.