We present the results of narrow-band Halpha+NII imaging of the early-type
spiral NGC3593 in combination with a study of the flux radial profiles of the
NII (lambda: 654.80, 658.34 nm), Halpha, and SII (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 Halpha emission mainly derives from a small central region of 57 arcsec x
25 arcsec. It consists of a filamentary pattern with a central ring. This has a
diameter of about 17 arcsec (~ 0.6/h kpc) and it contributes about half of the
total Halpha 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.Comment: Accepted for pubblication in Astronomy and Astrophysics; one latex
file (corsini.tex), and 2 encapsulated postscript figures
(corsini_fig1.ps,corsini_fig2.ps). To be compiled with aa.cls latex2e macro
style (pslatex option): 6 pages after latex compilatio
