ACA CO(J = 2–1) Mapping of the Nearest Spiral Galaxy M33. I. Initial Results and Identification of Molecular Clouds
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Triangulum GalaxyLocal GroupMolecular cloudsInterstellar medium
Kazuyuki Muraoka et al 2023. ACA CO(J = 2–1) Mapping of the Nearest Spiral Galaxy M33. I. Initial Results and Identification of Molecular Clouds. ApJ 953 164. [DOI 10.3847/1538-4357/ace4bd]
SponsorshipALMA: NAOJ-ALMA-289; ALMA Japan Research Grant of NAOJ ALMA Project NAOJ-ALMA-289; NAOJ ALMA Scientific Research 2022-22B; Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT) Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research (KAKENHI) JP18H05440, JP19H05075, JP21H00049, JP21H01136, JP21K13962
We present the results of ALMA-ACA 7 m array observations in (CO)-C-12(J = 2-1), (CO)-C-13(J = 2-1), and (CO)-O-18(J = 2-1) line emission toward the molecular-gas disk in the Local Group spiral galaxy M33 at an angular resolution of 7.& DPRIME;31 x 6.& DPRIME;50 (30 x 26 pc). We combined the ACA 7 m array (CO)-C-12(J = 2-1) data with the IRAM 30 m data to compensate for emission from diffuse molecular-gas components. The ACA+IRAM combined (CO)-C-12(J = 2-1) map clearly depicts the cloud-scale molecular-gas structure over the M33 disk. Based on the ACA+IRAM (CO)-C-12(J = 2-1) cube data, we cataloged 848 molecular clouds with a mass range from 10(3)-10(6) M (& ODOT;). We found that high-mass clouds (& GE;10(5) M (& ODOT;)) tend to associate with the 8 & mu;m bright sources in the spiral arm region, while low-mass clouds (M (& ODOT;)) tend to be apart from such 8 & mu;m 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.