Radio continuum contours from the narrow-band 21-cm of NGC 3998 overlaid on the continuum-subtracted Hα image from Sánchez-Gallego et al. (2012). The contours are described in Fig. 1. On the left we show a depiction of the position angles of the various galaxy components. Green-dashed: stars (PA ~135°, from Krajnović et al. 2011), black-solid: inner ~5 kpc of radio continuum (PA ~33°), blue-dotted: H i disk (PA ~65°), red-dot-dash: Hα disk (PA ~84°).