Radio continuum contours from the narrow-band 21 cm observations of NGC 3998 using the Westerbork Synthesis Radio Telescope overlaid on the continuum-subtracted Hα image from Sánchez-Gallego et al. (2012). On the left, we show a depiction of the position angles of the various galaxy components. The green dashed line represents stars (PA ∼ 135° from Krajnović et al. 2011), the black solid line the inner ∼5 kpc of the radio continuum (PA ∼ 33°), the blue dotted line the H I disc (PA ∼ 65°), and red dot-dashed line the Hα disc (PA ∼ 84°). The image is taken from Frank et al. (2016).