Dissemin is shutting down on January 1st, 2025

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American Astronomical Society, Astrophysical Journal, 2(953), p. 164, 2023

DOI: 10.3847/1538-4357/ace4bd

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ACA CO(J = 2–1) Mapping of the Nearest Spiral Galaxy M33. I. Initial Results and Identification of Molecular Clouds

This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

Abstract We present the results of ALMA-ACA 7 m array observations in 12CO(J = 2–1), 13CO(J = 2–1), and C18O(J = 2–1) line emission toward the molecular-gas disk in the Local Group spiral galaxy M33 at an angular resolution of 7.″31 × 6.″50 (30 × 26 pc). We combined the ACA 7 m array 12CO(J = 2–1) data with the IRAM 30 m data to compensate for emission from diffuse molecular-gas components. The ACA+IRAM combined 12CO(J = 2–1) map clearly depicts the cloud-scale molecular-gas structure over the M33 disk. Based on the ACA+IRAM 12CO(J = 2–1) cube data, we cataloged 848 molecular clouds with a mass range from 103–106 M . We found that high-mass clouds (≥105 M ) tend to associate with the 8 μm bright sources in the spiral arm region, while low-mass clouds (<105 M ) tend to be apart from such 8 μm bright sources and to exist in the inter-arm region. We compared the cataloged clouds with GMCs observed by the IRAM 30 m telescope at 49 pc resolution (IRAM GMC), and found that a small IRAM GMC is likely to be identified as a single molecular cloud even in ACA+IRAM CO data, while a large IRAM GMC can be resolved into multiple ACA+IRAM clouds. The velocity dispersion of a large IRAM GMC is mainly dominated by the line-of-sight velocity difference between small clouds inside the GMC rather than the internal cloud velocity broadening.