TNFALLING GAS TOWARD THE GALACTIC CENTER

摘要

VLA maps of ammonia emission were made for the Galactic center region. The NH-3(1, l) and NH-3(2, 2) transitions were observed in three 2' x 2' fields covering Sgr A* and the region 3' immediately south of it. In the central 3 pc surrounding Sgr A* we find emission that appears to be associated with the cir- cumnuclear disk (CND), both morphologically and kinematically. This central emission is connected to a long, narrow 2 pc x 10 pc streamer of clumsy molecular gas located toward the south, which appears to be carrying gas from the nearby 20 km s~-1 giant molecular cloud (GMC) to the circumnuclear region. We find a velocity gradient along the streamer, with progressively higher velocities as the gas approaches Sgr A*. The streamer stops at the location of the CND, where the line width of the NH~-3, emission increases dramatically. This may be the kinematic signature of accretion onto the CND. The ratio of the NH-3(2, 2)/NH-3,(1, 1) emission indicates that the gas is heated at the northern tip of the streamer, located inside the eastern edge of the CND. The morphology, kinematics, and temperature gradients of the gas all indicate that the southern streamer is located at the Galactic center and is interacting with the cir- cumnuclear region.