2022ApJ...938..145B

We present maps of four Galactic giant molecular clouds (GMCs) in the J = 2-1 emission of both CO and ¹³CO. We use an LTE analysis to derive maps of the CO excitation temperature and column density and the distribution of total molecular gas column density, Σ_gas. The depletion of CO by freeze-out onto cold dust grains is accounted for by an approximation to the results of Lewis et al., which were derived from far-IR observations with Herschel. The surface density of young stellar objects (YSOs) is obtained from published catalogs. The mean YSO surface density exhibits a power-law dependence on Σ_gas, with exponents in the range 0.9-1.9. Gas column density probability distribution functions show power-law tails extending to high column densities. The distributions of sonic Mach number, M_S, are sharply peaked at M_S ∼ 5-8 for 3 GMCs; a fourth has a broad distribution up to M_S = 30, possibly a result of feedback effects from multiple OB stars. An analysis following the methodology of Pokhrel et al. finds that our sample of GMCs shows power-law relations that are somewhat shallower than those found by Pokhrel et al. for the star formation rate versus 〈Σ_gas〉 and versus 〈Σ_gas〉/t_ff in a different sample of clouds. We discuss possible differences in the two samples of star-forming clouds and the effects of stellar feedback on the relation between gas density and star formation rate.