A molecular cloud and an expanding cavity adjacent to the nonthermal filaments of the Galactic center radio arc

Lar,ge-scale CO images taken with the 2 x 2 focal-plane array receiver on the 45 m telescope of Nobeyama Radio Observatory reveal parsec-scale structure of molecular gas around the Galactic center radio are. The LVG analysis shows that the gas kinetic temperature is considerably enhanced (T-k greater than or equal to 70 K) in CO 0.13-0.13, a cloud which seems to be in contact with the nonthermal filaments of the Galactic center radio arc. This lends support for an interaction between CO 0.13-0.13 and the nonthermal filaments. The interaction with the strong magnetic field in and around the nonthermal filaments may heat up the molecular gas in CO 0.13-0.13 through shock dissipation and/or magnetic viscosity. We also find an expanding cavity adjacent to the nonthermal filaments. The shell has a radius of similar to 5pc and an expansion velocity of 25 kms(-1). This expanding cavity might have been formed by several hundred supernovae or a single hypernova within 3 x 10(5) yr. Magnetic tubes in this region could have been swept up by the expanding cavity, and compressed by interactions with CO 0.13-0.13. An interaction between the cloud and magnetic field may accelerate electrons to relativistic energies through shock acceleration or magnetic field reconnection.