SCALING RELATIONS OF THE PROPERTIES FOR CO RESOLVED STRUCTURES IN NEARBY SPIRAL GALAXIES

Abstract

We report high spatial resolution observations of Giant Molecular Clouds (GMCs) in the nearby spiral galaxies NGC 6946, M101 and NGC 628 obtained with the CARMA telescope. We observed CO(1-0) over regions with active star formation, and higher resolution observations of CO(2-1) have allowed us to resolve some of the largest GMCs. Using a Bayesian fitting approach, we generate scaling relations for the sizes, line widths, and virial masses of the structures identified in this work. We do not find evidence for a tight power law relation between size and line width, although the limited dynamic range in cloud size remains a clear issue in our analysis. Additionally, we use a Bayesian approach to analyze the Kennicutt-Schmidt (K-S) relation for the identified structures. We find that the distribution of slopes are broadly distributed, mainly due to the limited dynamic range of our measured H2 mass surface density, and being most consistent with super-linear relations. On the other hand, when we use the Bayesian approach to analyze the K-S relation for a uniform grid, the distributions of slopes is consistent with sub-linear relations. On-arm regions tend to have higher star formation rates than inter-arm regions. As in NGC 6946, in M101 we find regions where the star formation efficiency shows marked peaks at specific galoctocentric radii. On the other hand, the distribution of SFE in NGC 628 is more contiguous. We hypothesize that differences in the distribution of SFE may be indicative of different processes driving the spiral structure.