Variation in GMC Association Properties across the Bars, Spiral Arms, Inter-arms, and Circumnuclear Region of M100 (NGC 4321) Extracted from ALMA Observations

Abstract

Abstract We study the physical properties of giant molecular cloud associations (GMAs) in M100 (NGC 4321) using the ALMA Science Verification feathered (12 m+ACA) data in 12CO (1–0). To examine the environmental dependence of their properties, GMAs are classified based on their locations in various environments as circumnuclear ring (CNR), bar, spiral, and inter-arm GMAs. The CNR GMAs are massive and compact, while the inter-arm GMAs are diffuse, with low surface density. GMA mass and size are strongly correlated, as suggested by Larson. However, the diverse power-law index of the relation implies that the GMA properties are not uniform among the environments. The CNR and bar GMAs show higher velocity dispersion than those in other environments. We find little evidence for a correlation between GMA velocity dispersion and size, which indicates that the GMAs are in diverse dynamical states. Indeed, the virial parameter of the GMAs spans nearly two orders of magnitude. Only the spiral GMAs are generally self-gravitating. Star formation activity decreases in order over the CNR, spiral, bar, and inter-arm GMAs. The diverse GMA and star formation properties in different environments lead to variations in the Kennicutt–Schmidt relation. A combination of multiple mechanisms or gas phase change is necessary to explain the observed slopes. Comparisons of GMA properties acquired with the use of the 12 m array observations with those from the feathered data are also presented. The results show that the missing flux and extended emission cannot be neglected for the study of environmental dependence.