The HASHTAG project II. Giant molecular cloud properties across the M31 disc

Deng, Yikai, Li, Zongnan, Li, Zhiyuan, Liu, Lijie, Ren, Zhiyuan, Athikkat-Eknath, Gayathri, de Grijs, Richard, Eales, Stephen A. ORCID: https://orcid.org/0000-0002-7394-426X, Eden, David J., Iono, Daisuke, Jiao, Sihan, Lee, Bumhyun, Li, Di, Saintonge, Amelie, Smith, Matthew W. L. ORCID: https://orcid.org/0000-0002-3532-6970, Tang, Xindi, Tsai, Chaowei, van der Giessen, Stefan A., Williams, Thomas G. and Wu, Jingwen 2025. The HASHTAG project II. Giant molecular cloud properties across the M31 disc. Monthly Notices of the Royal Astronomical Society 538 (4) , 2445–2462. 10.1093/mnras/staf455

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Abstract

We present a study of giant molecular cloud (GMC) properties in the Andromeda galaxy (M31) using CO(3-2) data from the James Clerk Maxwell Telescope (JCMT) in selected regions across the disc and in the nuclear ring, and comparing them with CO(1-0) observations from the IRAM 30m telescope in the same regions. We find that GMCs in the centre of M31 generally exhibit larger velocity dispersions (σ) and sizes (R) compared to those in the disc, while their average surface density (Σ) and turbulent pressure (Pturb) are lower. This low turbulent pressure in the central region is primarily due to the low density of molecular gas. The estimated GMC properties depend on the choice of CO transitions. Compared to CO(1-0), CO(3-2) exhibits smaller velocity dispersion and equivalent radius but higher surface density. These differences highlight the distinct physical conditions probed by different molecular gas tracers. We estimate the virial parameter αvir∝σ2R/Σ and find that most molecular clouds exhibit high values (αvir ∼ 4 − 6) for both CO transitions, indicating that they are unbound. Furthermore, clouds in the nuclear ring display even larger αvir values of ≲ 100, suggesting that they may be highly dynamic, short-lived structures, although they could potentially achieve equilibrium under the external pressure exerted by the surrounding interstellar medium.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Schools > Physics and Astronomy
Additional Information:	License information from Publisher: LICENSE 1: URL: https://creativecommons.org/licenses/by/4.0/, Start Date: 2025-03-20
Publisher:	Oxford University Press
ISSN:	0035-8711
Date of First Compliant Deposit:	1 April 2025
Date of Acceptance:	19 March 2025
Last Modified:	02 Apr 2025 11:16
URI:	https://orca.cardiff.ac.uk/id/eprint/177305

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