A REMARKABLE FEATURE IN THE GIANT EXTRAGALACTIC H-II REGION NGC 5471

We report the discovery of a very high velocity, low-intensity gas feature in the giant extragalactic H II region NGC 5471. A broad component in the emission lines of Hα + [N II] λλ6548, 6584 is located within an area less than 1″ in diameter at the position known as knot C. The broad component is characterized by its low intensity (less than 2% of the peak surface brightness in Hα), a contribution of ≈25% to the total flux of the lines, and an extension of ≈3300 km s-1 at full width at zero intensity (FWZI). Supernovae explosions and stellar winds are considered as possible sources of the gas motions, and the observational evidence for their presence is discussed.