2015ApJ...803...38I

I present high-resolution column density maps of two molecular clouds (MCs) having strikingly different star formation rates. To better understand the unusual, massive G216-2.5, an MC with no massive star formation, the distribution of its molecular gas is compared to that of the Rosette MC. Far-infrared data from Herschel are used to derive N(H₂) maps of each cloud and are combined with I_CO data to determine the CO-to-H₂ratio, X_CO. In addition, the probability distribution functions (PDFs) and cumulative mass fractions of the clouds are compared. For G216-2.5, <N(H₂)> = 7.8 x 10²⁰/cm2 and <X_CO> = 2.2 x 10²⁰/cm2 (K.km/s)^–1; for the Rosette, <N(H₂)> = 1.8 x 10²¹/cm2 and <X_CO> = 2.8 x 10²⁰/cm2 (K km/s)^–1. The PDFs of both clouds are log-normal for extinctions below ∼2 mag and both show departures from log-normality at high extinctions. Although it is the less-massive cloud, the Rosette has a higher fraction of its mass in the form of dense gas and contains 1389 M_☉ of gas above the so-called extinction threshold for star formation, A_v = 7.3 mag. The G216-2.5 cloud has 874 M_☉ of dense gas above this threshold.