Layout and detections of our ATCA HI survey. The green outline includes the 15-deg² region where the average noise is 2.8 mJy beam⁻¹ (see Sect. 2). The red contours represent the lowest reliable HI column density – 3σ over 25 km s⁻¹ – of our 16 detections. The grey dashed circle is R_vir. The background optical image comes from the Digital Sky Survey (blue band). The yellow contours show the X-ray emission in the Fornax cluster detected with XMM-Newton (Frank et al. 2013) and convolved with a 3 arcmin FWHM gaussian kernel. These contours are spaced by a factor of 2, with the lowest level at 3.7 counts deg⁻² s⁻¹.