Discovery of a Nearby Low Surface Brightness Spiral Galaxy

During the course of a search for compact, isolated gas clouds moving with anomalous velocities in or near our own Galaxy, we have discovered in the data of the Leiden/Dwingeloo survey of Galactic hydrogen the H I signature of a large galaxy moving at a recession velocity of 282 km s^-1 with respect to our Galaxy. Deep multicolor and spectroscopic optical observations show the presence of star formation in scattered H II regions; radio H I synthesis interferometry confirms that the galaxy is rich in H I and has the rotation signature of a spiral galaxy; a submillimeter observation failed to detect the CO molecule. The radio and optical evidence combined suggest its classification as a low surface brightness (LSB) spiral galaxy. It is located in close spatial and kinematic proximity to the galaxy NGC 6946. The newly discovered galaxy, which we call Cep 1, is at a distance of about 6 Mpc. It is probably to be numbered among the nearest few LSB spiral galaxies.