A Molecular Cloud and an Expanding Cavity Adjacent to the Nonthermal Filaments of the Galactic Center Radio Arc

Abstract

Abstract Large-scale CO images taken with the $2 \times 2$ 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 arc. The LVG analysis shows that the gas kinetic temperature is considerably enhanced ($T_\mathrm{k} \geq 70 \,\mathrm{K}$) 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 $\sim 5 \,\mathrm{pc}$ and an expansion velocity of $25 \,\mathrm{km} \,\mathrm{s}^{-1}$. This expanding cavity might have been formed by several hundred supernovae or a single hypernova within $3 \times 10^5 \,\mathrm{yr}$. 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.