Fig. 4. a (top): Grey scale image of the continuum-free Pa emission towards the center of NGC 3593, obtained from HST archive data Böker et al. (1999). Linear scale ranges from 1.4 10^-17 to 1.4 10^-16 erg cm ^-2 s^-1 pixel^-1. The dashed ellipse highlights the location of the starburst ring. b (bottom): Overlay of CO emission line contours (same levels as Fig. 2a) with the visual extinction map obtained from the hydrogen recombination lines ratio (grey scale from A_v=0 to A_v=2.5).