X-ray emission from ROSAT, tracing the thermal ICM, is shown by the color image. The original image from the ROSAT All Sky Survey was convolved with a 200″ FWHM Gaussian. Solid contours are from the WSRT 1382 MHz image and drawn at levels of [1,2,4,8,...] × 4σ_rms. The resolution of the WSRT image is 23.5″ × 17.0″. Dashed contours show the galaxy iso-density distribution derived from the INT images. Contours are drawn at [1,1.1,1.2,1.3,1.4...] × 0.38 galaxies arcmin^-2 using the color cuts as described in Sect. 3.2.