Molecular Gas Properties on Cloud Scales Across the Local Star-forming
  Galaxy Population
  Using the PHANGS-ALMA CO (2-1) survey, we characterize molecular gas
properties on ${\sim}$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 sub-resolution gas structure, the inferred virial
parameters suggest that the kinetic energy of the molecular gas typically
exceeds its self-gravitational binding energy at ${\sim}$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 towards 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.
