GBT26B-263

Structure of Diffuse Molecular Gas in OH and HCO+: Extending the Sample

Abstract

The discovery of apparently extremely broad diffuse gas in OH emission towards the Outer Galaxy (Busch et al. 2021) and HCO+ absorption towards high latitude objects (Rybarczyk et al. 2022), coincident with HI in either absorption or emission hints at the first phase of molecule formation in the ISM. A spectra towards B0355+508 showcasing these characteristics (kinematically broad, and weak molecular signal) was first discovered by Liszt and Lucas 2000. This phase space is completely dark in CO emission (and now we know, also in CO absorption), which makes mapping the structure of this apparently diffuse molecular gas incredibly difficult. This proposal is an extension of the proposal GBT24A_144 in which we performed extremely sensitive GBT measurements of OH towards three sources which had previously detected HCO+ absorption across a broad extent of velocity, coincident with HI absorption and also completely "CO-dark". We successfully detected faint OH emission with the GBT, with analysis underway to understand the structure of the distribution of the underlying gas from spectral domain alone. This proposal will observe two more sources to obtain OH spectra, completing our sample of 5 sources, from which we can compile individual decomposed cloud components for a statistical ensemble.

Investigators

Name	Institution
Michael Busch *	National Radio Astronomy Observatory
Joanne Dawson	Macquarie University; Commonwealth Scientific and Industrial Research Organisation
Daniel Rybarczyk	Wisconsin at Madison, University of
Harvey Liszt	National Radio Astronomy Observatory; National Institute of Flamenco; Belize, Pontifical University of
Maryvonne Gerin	Paris, Observatoire de

* indicates the PI