Interferometric (CO)-C-12 observations of the central disk of NGC 4631: Anenergetic molecular outflow

We present interferometric observations of CO J = 1-0 emission in the centr al regions of the edge-on galaxy NGC 4631, known for its extended gaseous h alo and its tidal interactions. Previous single-dish observations revealed that almost all of the CO emission arises from a central ring or barlike st ructure of length similar to 4 kpc. We confirm this structure at higher res olution and find that it is bent at the center, reflecting the overall bend in this galaxy apparent from optical images. The kinematic evidence favors a rigidly rotating ring over a bar. The gaseous halo emission in several t racers is concentrated above and below this molecular structure. To the nor th of an emission peak at the eastern end of the structure is an extraplana r feature showing filamentary and shell-like properties we interpret as an energetic molecular outflow. The energies involved are difficult to estimat e but are probably of order 10(54) ergs or more. The CO concentration in th e disk below this structure coincides with a bright H II region complex, a peak of radio emission, and the brightest X-ray feature in the inner disk o f the galaxy seen in a ROSAT HRI map, all suggesting intense star formation . A filament of radio continuum emission may also have a footprint in this region of the disk. The origin of the outflow is unclear.