Left: integrated (−37.3 ≤ v_LSR [ km s^-1 ] ≤ 52.9) GASS HI column density map of HRK 81.4–77.8. Superposed as contours is the Planck 857 GHz intensity distribution starting at 0.76 MJy sr^-1 in steps of 0.45 MJy sr^-1. Right: slice across the longest extent of HRK 81.4–77.8 (see left panel, dots along the solid line). The open triangles mark the HI column density distribution N_HI in 10¹⁸ cm^-2, the filled circles represent the ROSAT R12 count rate in 10^-6 cts s^-1 arcmin^-2.