The Equilibrium State of Molecular Regions in the Outer Galaxy

A summary of global properties and an evaluation of the equilibrium state of molecular regions in the outer Galaxy are presented from the decomposition of the FCRAO Outer Galaxy Survey and targeted ¹²CO and ¹³CO observations of four giant molecular cloud complexes. The ensemble of identified objects includes both small, isolated clouds and clumps within larger cloud complexes. The ¹²CO luminosity function and size distribution of a subsample of objects with well-defined distances are determined such that ΔN/ΔL_CO=(3×10⁴)L^{-1.80+/- 0.03}_CO and ΔN/Δr_e=(1.7×10⁴)r^{-3.2+/- 0.1}_e. ¹²CO velocity dispersions show little variation with cloud sizes for radii less than 10 pc. It is demonstrated that the internal motions of regions with M_CO=X_COL_CO>10⁴ M_solar are bound by self-gravity, yet the constituent clumps of cloud complexes and isolated molecular clouds with M_CO<10³ M_solar are not in self-gravitational equilibrium. The required external pressures to maintain the equilibrium of this population are (1-2)×10⁴ cm^-3 K.