HyGAL: Characterizing the Galactic Interstellar Medium with Hydrides
PI: David Neufeld (Johns Hopkins University) and Peter Schilke (University of Cologne)
Selected in Cycle 8
Proposal ID: 08_0038
Instrument: GREAT

Abstract Excerpt: By means of absorption-line spectroscopy towards 22 background Terahertz continuum sources widely distributed within the Galactic plane, we will obtain robust measurements of the column densities of six hydride molecules (OH+, H2O+, ArH+, SH, OH, and CH) and two key atomic constituents (C+ and O) within the diffuse ISM. These observations will allow us to address several related questions: (1) What is the distribution function of H2 fraction in the ISM? (2) How does the density of low-energy cosmic-rays vary within the Galaxy? (3) What is the nature of interstellar turbulence (e.g. typical shear or shock velocities), and what mechanisms lead to its dissipation?

The anticipated results are (1) a determination of the distribution function for the H2 fraction in the Galaxy, and how it varies; (2) a determination of the cosmic-ray ionization rate and how it varies; (3) an improved characterization of turbulence in the diffuse ISM, and its dissipation; (4) the provision of enhanced data products that will serve as a legacy for future ISM studies.

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