ACA CO(J=2-1) mapping of M33. I. Molecular clouds

We combined the ACA 7m array 12CO(J=2-1) data with the IRAM 30m data to compensate for emission from diffuse molecular-gas components. The ACA+IRAM combined ^12^CO(J=2-1) map clearly depicts the cloud-scale molecular-gas structure over the M33 disk.

Based on the ACA+IRAM ^12^CO(J=2-1) cube data, we cataloged 848 molecular clouds with a mass range from 10^3^-10^6^M_{sun}_. We found that high-mass clouds (>=10^5^M_{sun}_) tend to associate with the 8{mu}m bright sources in the spiral arm region, while low-mass clouds (<10^5^M_{sun}_) 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 30m telescope at 49pc 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.