Postdoctoral Fellowship: AAPF: All Shook Up: Understanding the Chemistry, Dynamics, and Kinematics of the Diffuse Interstellar Medium

Daniel Rybarczyk is awarded an NSF Astronomy and Astrophysics Fellowship to carry out a program of research and education at the University of Wisconsin–Madison. Rybarczyk will use radio/millimeter observations of atomic hydrogen (HI) and various molecular species to study the role of shocks in shaping the structure and chemistry of the diffuse interstellar medium (ISM). Rybarczyk will measure the abundances of these key ISM constituents in regions where molecule formation is just getting under way to understand the first steps in the process of molecular cloud formation, which plays a critical role in star formation and galaxy evolution. Rybarczyk will also conduct an outreach program hosting public school visits (with a focus on schools with students from groups historically underrepresented in STEM fields) to the University of Wisconsin–Madison's Astronomy Department, including its planetarium and Washburn Observatory. Recent work has argued that shocks are crucial to the physical and chemical evolution of the diffuse ISM, playing a vital role in the very first stages of the star formation process, but direct observations of shock tracers in these environments are rare. Rybarczyk will roughly triple the existing sample of diffuse sightlines with observations of the molecule SiO — generally believed to be an unambiguous tracer of interstellar shocks — in the diffuse ISM, targeting directions where shock chemistry is implied by indirect tracers or filamentary structure. These measurements and a comparison to non-equilibrium chemical model predictions will test our understanding of shock chemistry in a low-density regime largely unexplored in the existing literature. Further observations of the molecules HCO+ and CO will complement the SiO measurements, probing the molecular gas content of the diffuse ISM and testing our ability to detect diffuse molecular gas using different tracers. 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.