Evidence for Shocked Molecular Gas in the Galactic Supernova Remnant CTB 109 (G109.1-1.0)

We report the detection of molecular clouds around the X-ray-bright interior feature in the Galactic supernova remnant (SNR) CTB 109 (G109.1-1.0). This feature, called the ``lobe,'' has been previously suggested to be the result of an interaction of the SNR shock wave with a molecular cloud complex. We present new high-resolution X-ray data from the Chandra X-Ray Observatory and new high-resolution CO data from the Five College Radio Astronomy Observatory that show the region of interaction with the cloud complex in greater detail. The CO data reveal three clouds around the lobe in the velocity interval -57 km s^-1<v<-52 km s^-1. The velocity profiles of ¹²CO in various parts of the east cloud are well fit with a Gaussian; however, at the position at which the CO cloud and the lobe overlap, the velocity profile has an additional component toward higher negative velocities. The molecular hydrogen density in this part of the cloud is relatively high (N_H2~1.9×10²⁰ cm^-2), whereas the foreground absorption in X-rays (N_H~4.5×10²¹ cm^-2), obtained from Chandra data, is lower than in other parts of the cloud and in the north and south clouds. These results indicate that the east cloud has been hit by the SNR blast wave on the western side, forming the bright X-ray lobe.