SIMBAD references

Using the IRAM 30 m telescope, we observed the supernova remnant 3C 391 (G31.9+0.0) and its surroundings in the ¹²CO (2⟶1), HCO⁺ (1⟶0), CS (2⟶1), CS (3⟶2), and CS (5⟶4) lines. The ambient molecular gas at the distance (9 kpc) of the remnant comprises a giant molecular cloud whose edge is closely parallel to a ridge of bright nonthermal radio continuum, which evidently delineates the blast wave into the cloud. We found that in a small (0.6 pc) portion of the radio shell, the molecular line profiles consist of a narrow (2 km.s^–1) component plus a very wide (greater than 20 km.s^–1) component. Both spectral components peak within 20" of a previously detected OH 1720 MHz maser. We name this source 3C 391:BML (broad molecular line); it provides a new laboratory, similar to IC 443 but on a larger scale, to study shock interactions with dense molecular gas. The wide spectral component is relatively brighter in the higher excitation lines. We interpret the wide spectral component as postshock gas, either smoothly accelerated or partially dissociated and reformed behind the shock. The narrow component is either the preshock gas or cold gas reformed behind a fully dissociative shock. Using the three observed CS lines, we measured the temperature, CS column density, and H₂ volume density in a dense clump in the parent molecular cloud, as well as the wide-line and narrow-line portions of the shocked clump. The physical conditions of the narrow-line gas are comparable to the highest density clumps in the giant molecular cloud, while the wide-line gas is both warmer and denser. The mass of compressed gas in 3C 391:BML is high enough that its self-gravity is significant, and eventually it could form one or several stars.