The Properties of Bound and Unbound Molecular Cloud Populations Formed
  in Galactic Disc Simulations
  We explore the effect of galactic environment on properties of molecular
clouds. Using clouds formed in a large-scale galactic disc simulation, we
measure the observable properties from synthetic column density maps. We
confirm that a significant fraction of unbound clouds forms naturally in a
galactic disc environment and that a mixed population of bound and unbound
clouds can match observed scaling relations and distributions for extragalactic
molecular clouds. By dividing the clouds into inner and outer disc populations,
we compare their distributions of properties and test whether there are
statistically significant differences between them. We find that clouds in the
outer disc have lower masses, sizes, and velocity dispersions as compared to
those in the inner disc for reasonable choices of the inner/outer boundary. We
attribute the differences to the strong impact of galactic shear on the disc
stability at large galactocentric radii. In particular, our Toomre analysis of
the disc shows a narrowing envelope of unstable masses as a function of radius,
resulting in the formation of smaller, lower mass fragments in the outer disc.
We also show that the star formation rate is affected by the environment of the
parent cloud, and is particularly influenced by the underlying surface density
profile of the gas throughout the disc. Our work highlights the strengths of
using galaxy-scale simulations to understand the formation and evolution of
cloud properties - and the star formation within them - in the context of their
environment.
