Constant-column-density H I contours overlaid on the g-band CFHT/MegaCam image. The colour bar on the right is in mag arcsec− 2. Contours represent N(H I) = 1.0 × 1019 × 3n cm− 2 (n = 0, 1, 2, 3). Contours are coloured black to red, faint to bright. The black cross indicates the pointing centre of our WSRT observation and the dotted, black circle indicates the primary beam of the WSRT. Large and small dashed, red circles indicate the location of TN and CS, respectively (see text). The beam of the H I image is shown on the bottom-left corner. Note that UGC 05574 (to the north-east) and SDSS J1017 (to the south-west) are not members of HCG 44.
(Serra et al., 2013)