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SFB Colloquium |
Dr. Nick Indriolo
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Johns Hopkins University, Baltimore
Chemical complexity in the molecular interstellar medium (ISM) is driven by fast ion-molecule reactions. This network of chemical reactions requires a source of ionization, and as molecular gas is generally well-shielded from ionizing UV photons, cosmic rays provide the dominant source of ionization in such environments. The impact of cosmic rays on atomic and molecular hydrogen is parameterized as the cosmic-ray ionization rate (CRIR; number of ionizations per atom/molecule per unit time), which serves as an important input variable in astrochemical modeling. Our understanding of cosmic rays in both diffuse and dense gas has vastly improved over the past decade as more detailed chemical models have been developed, and as more sensitive observations of molecules that respond to the CRIR have been made. The recent creation of 3D dust maps using Gaia differential extinction measurements allows, for the first time, ionization rates inferred from observations of molecular absorption lines to be assigned to a physical location in the nearby Galaxy. By combining this information we are beginning to build the first map of the CRIR in the solar neighborhood. I will discuss our ongoing work on this project, and how we can use such a map to better understand cosmic-ray acceleration and propagation.