The circumnuclear ring of ionized gas in NGC 3593

We present the results of narrow-band H alpha+[N II] imaging of the early-type spiral NGC 3593 in combination with a study of the flux radial profiles of the [N II] (lambda lambda 654.80, 658.34 nm), H alpha, and [S II] (lambda lambda 671.65, 673.08 nm) emission lines along its major axis. The galaxy is known to contain two counterrotating stellar discs of different size and luminosity. We find that the Her emission mainly derives from a small central region of 57 " x 25 ". It consists of a filamentary pattern with a central ring. This has a diameter of about 17 " (similar to 0.6 h(-1) kpc) and it contributes about half of the total H alpha flux. The ring is interpreted as the result of the interaction between the acquired retrograde gas which later formed the smaller counterrotating stellar disc and the pre-existing prograde gas of the galaxy.