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Paper: NRO M33 All-Disk Survey of Giant Molecular Clouds (NRO MAGiC): Properties of Giant Molecular Clouds in M33
Volume: 476, New Trends in Radio Astronomy in the ALMA Era
Page: 303
Authors: Onodera, S.; Kuno, N.; Tosaki, T.; Muraoka, K.; Miura, R.; Kohno, K.; Nakanishi, K.; Sawada, T.; Komugi, S.; Kaneko, H.; Hirota, A.; Kawabe, R.
Abstract: We present the results of the CO-line mapping observations of the local group galaxy M33 as part of the NRO legacy project, NRO M33 All-Disk Survey of Giant Molecular Clouds (NRO MAGiC). The observations were performed using the 45-m telescope of the Nobeyama Radio Observatory and the ASTE 10-m telescope. We find that the star formation rate have very wide range of 109–106 M☉ yr-1pc–2 among GMCs, while 12CO(J=1–0) intensity is nearly constant. This indicates that the Schmidt-Kenicutt law becomes invalid for the scale of GMCs (∼80pc). We identify 74 major GMCs in the observing field of ASTE from the 12CO(J=1–0) data, and detected 12CO(J=3–2) emission in 65 GMCs among them. We find that the correlation between the 12CO(J=3–2) intensity and the star formation rate still holds at the scale of GMCs. This result show that the star-forming activity is closely associated with warm and dense gases that are traced with the 12CO(J=3–2) line, even in the scale of GMCs. We also find that the GMCs with a high star-forming activity tend to show a high integrated intensity ratio R3–2/1–0. Moreover, we also observe a mass-dependent trend of R3–2/1–0 for the GMCs with a low star-forming activity. From these results, we speculate that the R3–2/1–0 values of the GMCs with a low star-forming activity mainly depend on the dense gas fraction and not on the temperature, and therefore, the dense gas fraction increases with the mass of GMCs, at least in the GMCs with a low star-forming activity.
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