Left: three-color IRAC image (blue is the 3.6 μm, green the 4.5 μm and red the 8 μm band) of HCG 57a (southern object) and 57d (northern object). The circles represent the positions detected in CO(1–0). The size of the circles corresponds to the FWHM size of the IRAM 30 m beam at the frequency of CO(1–0). The large yellow rectangle shows, for reference, the size of the zoomed image at the right. The small red rectangle is the position where extragalactic, warm H₂ was detected by Cluver et al. (2013). Right: the detected CO(1–0) (blue) and CO(2–1) (green) spectra at these positions, overlaid over an IRAC 3.5 μm image. The velocity range is from 8000 to 10 000 km s^-1 for all spectra.