Abstract
Abstract Using the PHANGS–ALMA CO(2–1) survey, we characterize molecular gas properties on ∼100 pc scales across 102,778 independent sightlines in 70 nearby galaxies. This yields the best synthetic view of molecular gas properties on cloud scales across the local star-forming galaxy population obtained to date. Consistent with previous studies, we observe a wide range of molecular gas surface densities (3.4 dex), velocity dispersions (1.7 dex), and turbulent pressures (6.5 dex) across the galaxies in our sample. Under simplifying assumptions about subresolution gas structure, the inferred virial parameters suggest that the kinetic energy of the molecular gas typically exceeds its self-gravitational binding energy at ∼100 pc scales by a modest factor (1.3 on average). We find that the cloud-scale surface density, velocity dispersion, and turbulent pressure (1) increase toward the inner parts of galaxies, (2) are exceptionally high in the centers of barred galaxies (where the gas also appears less gravitationally bound), and (3) are moderately higher in spiral arms than in inter-arm regions. The galaxy-wide averages of these gas properties also correlate with the integrated stellar mass, star formation rate, and offset from the star-forming main sequence of the host galaxies. These correlations persist even when we exclude regions with extraordinary gas properties in galaxy centers, which contribute significantly to the inter-galaxy variations. Our results provide key empirical constraints on the physical link between molecular cloud populations and their galactic environment.
Highlights
Observations indicate that the physical properties of giant molecular clouds (GMCs) vary systematically with their location in a galaxy
In this Letter, we report measurements of the cloud-scale molecular gas surface density and velocity dispersion, as well as estimates of the turbulent pressure and the virial parameter
We investigate whether galaxy morphological features, i.e., stellar bars and spiral arms, have an impact on the molecular gas properties on cloud scales
Summary
Observations indicate that the physical properties of giant molecular clouds (GMCs) vary systematically with their location in a galaxy This result is obtained in the Milky Way (e.g., Rice et al 2016; Roman-Duval et al 2016; MivilleDeschênes et al 2017; Colombo et al 2019, but see Lada & Dame 2020) and in other galaxies (e.g., Donovan Meyer et al 2013; Hughes et al 2013a; Colombo et al 2014a; Leroy et al 2016; Schruba et al 2019). The derived measurements constitute a benchmark data set that can be readily compared with observations of other types of galaxies or numerical simulations reaching similar spatial resolutions (e.g., Semenov et al 2018; Dobbs et al 2019; Fujimoto et al 2019; Jeffreson et al 2020)
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