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 d ata of the Leiden/Dwingeloo survey of Galactic hydrogen the H I signature o f a large galaxy moving at a recession velocity of 282 km s(-1) with respec t to our Galaxy. Deep multicolor and spectroscopic optical observations sho w the presence of star formation in scattered H II regions; radio H I synth esis interferometry confirms that the galaxy is rich in H I and has the rot ation signature of a spiral galaxy; a submillimeter observation failed to d etect the CO molecule. The radio and optical evidence combined suggest its classification as a low surface brightness (LSB) spiral galaxy. It is locat ed in close spatial and kinematic proximity to the galaxy NGC 6946. The new ly 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.