University of Connecticut

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Astronomy Seminar

Wednesday, October 9, 2019
2:00pm – 3:00pm

Storrs Campus

Philip Engelke, Department of Physics and Astronomy, Johns Hopkins University

OH as an Alternate Tracer for Molecular Gas

While molecular gas is an important component of the baryonic mass content of galaxies, tracing interstellar molecular H2 gas is complicated by the fact that diffuse, cold H2 is not detectable. In order to study the mass and distribution of molecular gas in galaxies, tracers such as CO are typically used as surrogates. Evidence suggests large reservoirs of undetected "CO-dark" molecular gas. In this work, we explore the use of OH 18 cm transition as an alternate tracer for molecular gas, by performing observational surveys with the Green Bank Telescope. OH appears to be a viable tracer, and reveals molecular gas in places where CO has not been detected. This finding indicates a larger extent and mass of molecular gas in the Galaxy, translating to roughly twice the known mass of H2. I will describe our results for a "blind survey", as well as a study of the W5 star-forming region in comparison to quiescent interstellar regions, and modeling of the volume density in these different regions. We find that CO-dark molecular gas is widespread and predominantly located outside of star-forming regions, the more typical targets of astronomical observation, and occurs in regions of lower volume density gas. I also describe a technique making use of measured differences in OH main line excitation temperatures and modeling to probe physical conditions of molecular gas.


A. Huang

Physics Department (primary), College of Liberal Arts and Sciences

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