The Role of Global and Local Environments in Shaping GMC Properties: A High Resolution Case Study of NGC 300
Chris Faesi
Thursday December 4th, 10:55
Giant Molecular Clouds (GMCs) are the cradles of stellar birth across the Universe. GMCs in the Milky Way exhibit remarkable uniformity in their physical structure (e.g., Lombardi et al. 2010, Heyer \& Dame 2015), while recent observations of nearby galaxies have suggested that GMC properties vary with environment (e.g., Colombo et al. 2014; Utomo et al. 2015). To further explore the role of local environment on GMCs, I have led a series of high-resolution, high-sensitivity investigations into molecular gas and star formation in NGC~300, a nearby, low mass, half-solar metallicity spiral galaxy that at a distance of 2 Mpc provides an ideal laboratory for resolved GMC studies and comparison to the Milky Way and other galaxies (Faesi et al. 2014, 2016, 2018). In this presentation, I will describe the results of our CO(2-1) ALMA study in which we achieve 10 pc and 1 km/s resolution, fully resolving GMCs scales and detecting 250 clouds at high signal-to-noise. I will show that despite large differences between global properties of the Milky Way and NGC 300, the GMC populations in these galaxies are consistent with the same Larson (1981) relations (size-linewidth, virial, mass-size) and a similar mass spectrum slope and mass cutoff (see Figure). Disk midplane pressure, which is similar between the Milky Way and NGC 300, may explain observed differences in GMC properties in other galaxies such as M51, as well as in more extreme physical environments such as the Galactic Center. I will conclude by showing first results from the PHANGS (Physics at High Angular resolution in Nearby Galaxies) project in which we are using ALMA observations to resolve GMC scales across the disks of 70 nearby spiral galaxies. These follow-up studies are confirming the central role of pressure in setting GMC properties in spiral galaxies across the star-forming main sequence (Sun et al. 2018).