GBT25A-129

A Survey for OH in the Northern Molecular Ring of M31

Abstract

M31 is our largest, nearest neighboring galaxy that can be observed from the northern hemisphere. Recently, Busch 2024 announced the detection of ground-state thermal 18cm OH in the southern disk of M31 at a galactocentric distance of ~13 kpc using the GBT. While thermal OH is faint (~a few mK per channel), it remains our only reliable tracer for "CO-dark" diffuse molecular gas in the radio regime and thus easily accessible from the ground in any weather conditions.

While we await a new phased-array feed with many simultaneous beams, like ALPACA, we now propose to expand the number of extragalactic thermal OH detections and explore the usage of the OH line in M31 as a bulk tracer of molecular gas as compared to CO. We propose a new grid survey of the northern molecular ring of M31, which includes both reliable CO detections and non-detections. This will allow direct comparisons of column densities, linewidths, detailed dust extinction mapping comparisions and potentially detect "CO-dark" gas in the transition region from the atomic HI to dense CO bright gas.

Investigators

Name	Institution
Michael Busch *	California at San Diego, University of

* indicates the PI