150 GHz NOBA Observations of the Galactic Center Arc

Abstract

We have used the seven-beam 150 GHz bolometer NOBA installed at the Nobeyama 45-m telescope to map the central section of the Galactic Center Arc. In addition, we mapped Sgr A, which shows Sgr A* and the thermal spiral structure. The results agree with previous mm-observations. South of the thermal “sickle” feature (G0.18-0.04) we observed three regions of enhanced emission along the Arc, which are located slightly offset relative to the most intense vertical filaments seen at low frequencies. This 150 GHz emission is observed at the apparent interacting areas of dense molecular material with the Arc. Another structure is seen south of the molecular cloud, where the Arc's vertical filaments apparently cross a weak filamentary structure running orthogonally in the direction of Sgr A. The 150 GHz results are unexpected in view of previous 32 GHz and 43 GHz results, which indicate a fading of the Arc towards higher frequencies. Cold dust can be ruled out as the origin of the 150 GHz emission. Synchrotron emission from quasi-monoenergetic electrons or an electron distribution with a low-energy cut-off seems to be compatible with the available data. The coincidence of enhanced emission with regions of interacting molecular gas strongly suggests that high-energy electrons are accelerated in those places where the magnetic field is compressed, and subsequently enter and illuminate the Arc.