Structures of GMC W 37

Abstract

We carried out observations toward the giant molecular cloud W 37 with the J = 1 − 0 transitions of 12CO, 13CO and C18O using the 13.7m single-dish telescope at the Delingha station of Purple Mountain Observatory. Based on these CO lines, we calculated the column densities and cloud masses for molecular clouds with radial velocities around +20 km s−1. The gas mass of W 37, calculated from 13 CO emission, is 1.7 × 105 M⊙, above the criterion to be considered a giant molecular cloud. The dense ridge of W 37 is a dense filament, which is supercritical in terms of linear mass ratio. Dense clumps found by C18O emission are aligned along the dense ridge at regular intervals of about 2.8 pc, similar to the clump separation caused by large-scale ‘sausage instability’. We confirm the identification of the giant molecular filament (GMF) G 18.0-16.8 and find a new giant filament, G 16.5−15.8, located ∼ 0.7° to the west of G 18.0−16.8. Both GMFs are not gravitationally bound, as indicated by their low linear mass ratio (∼ 80 M⊙ pc−1). We compared the gas temperature map with the dust temperature map from Herschel images, and found similar structures. The spatial distributions of class I objects and the dense clumps are reminiscent of triggered star formation occurring in the northwestern part of W 37, which is close to NGC 6611.