Panel a: HST/ACS F814W (i-band; Koekemoer et al. 2007), panel b: HST/WFC3 F160W (Faisst et al., in prep.), and panel c: UltraVISTA DR4 Ks-band (McCracken et al. 2012) images of the system. The rest-frame UV positions of VC_9780 (dubbed #A) and C15_705574 (dubbed #B) are highlighted with a yellow square in panel a. The grey contour indicates the extension of the full [CII]-emitting region (see Sect. 3.3). The white bar shows a reference length of 15 kpc. North is up and east is to the left.