GBT26A-319

Dense gas in the Cold GMCs Discovered in M31 Inter-arm Regions

Abstract

We have newly identified a population of cold, giant molecular clouds (GMCs) in the inter-arm regions of M31. This is the first time such cold, inter-arm GMCs have been found in dust emissions in spiral galaxies. Follow-up observations reveal that these inter-arm GMCs have systematically lower masses and dust temperatures than those of on-arm GMCs in M31 or GMCs in the Milky Way, and their CO (1-0) emission linewidth is lower than the average CO linewidth of on-arm GMCs. These inter-arm GMCs are cold, quiescent, with sizes up to ~50 pc. The distinct properties make them extremely interesting objects to study in detail, as they are likely a different type of GMCs that may have different origin as to typical GMCs. We propose to use 20 hours of GBT observations to follow up five inter-arm GMCs with ammonia emission lines, aiming to reveal their dense gas properties and their potential to form massive stars. This observation will provide critical information on dense gas fraction and possibly gas temperatures of this new population of GMCs. This is a resubmission of a GBT ranking A proposal in 2025A, which was not scheduled due to time limitation.

Investigators

Name	Institution
Yuxiang Liu *	Chinese Academy of Sciences, University of
Sihan Jiao	National Astronomical Observatories, CAS
Jingwen Wu	California at Los Angeles, University of; National Astronomical Observatories, CAS

* indicates the PI