Total intensity image of M 51 at 3 GHz with a resolution of 10″ × 7″, shown as contours, overlaid onto a Hα image (Kennicutt et al. 2003) (left) and with a resolution of 15″ in color scale in units of Jy beam⁻¹ (right). The contours are drawn at [8, 16, 32, 64, 128, 256]  ×  30 μJy beam⁻¹ (left). The beam size is shown in the top left corner. We note that this is the Stokes I image from only one spectral window that has a bandwidth of about 100 MHz (see Sect. 3.1 for explanation).