The Nature of the Dark, Diffuse Interstellar Medium in the Local Group

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Michael Busch is awarded an NSF Astronomy and Astrophysics Fellowship to carry out a program of research and education at the University of California, San Diego. Busch will perform radio astronomical observations of the hydroxyl radical (OH) to study the properties and molecular hydrogen (H2) content of the interstellar medium (ISM) of nearby galaxies. The observations will complement observations of carbon monoxide (CO) – a widely used probe of H2 – to shed light on “dark H2” gas that cannot be studied using CO, as well as those of atomic hydrogen (HI). Results from the study will allow astronomers to understand how atomic gas undergoes the transition to molecular gas. For the education component of this project, Busch will develop a workshop on using a portable planetarium to increase astronomy engagement with grade school students.This research project will generate large maps of OH allowing reliable inference of the distribution of diffuse dark H2 in two representative local group galaxies. Combined with CO and HI observations, this will enable a thorough characterization of the environment, mass, and kinematics of the ISM. The observations and analyses will help elucidate the nature of dark H2 in unprecedented detail, yielding unique insight into the transition between the atomic and molecular gas in the ISM. Data from this project will also be useful for studies of astrochemistry, star formation, and galactic structure.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.