PACS images of I Zw 18 superimposed as contours on the F606W HST/ACS image shown with false colors. From left to right are PACS 70, 100, and 160 μm. Contours start at 3σ, and run to 7σ for PACS 70, to 16σ for PACS 100, and for PACS 160 to 2σ. As in Fig. 2, these σ values correspond to the correlated noise measured from the images, which are smaller than the true noise (see text).