Left panel: VLA H I column density contours overlaid on the V-band image of JO201 from WINGS. Contour levels are drawn at column densities of 4, 8, 12, ... × 10¹⁹ atoms cm⁻². The FWHM beam size of 16″ × 25″ is indicated by the blue ellipse. The red contours represent the stellar disc and the black contour is the H I disc (see text for a definition). Right panel: Hα emission with H I column density contours (same levels as the left panel) overlaid. The red opaque patch is the stellar disc and the black contour is the H I disc. The black circle is the region over which we estimate the H I flux density as described in the text.