A unified image of dust grains for the warped spiral galaxy in the merger Centaurus A ?

A unified view of dust grains of all sizes and temperatures in Centaurus A has been generated by combining ISOCAM mid-infrared images with optical data. In our unified V-15μm ratio image, a symmetrical bar-like structure and spiral arms of size 1.5 kpc surround the nucleus. We have overlaid the (H-K) model colour map of Quillen et al. (1993) and find a striking correspondence with the ridges seen in emission 15 μm and the dark lanes which they find in the near-infrared. The inference is that the morphology of large cold dust grains, responsible for the extinction at V, H and K, closely follows that of the hot dust over the full projected 3kpc diameter of the mini-spiral galaxy. From the spatial distribution of our V-15μm map, we derive a dust mass of approximately 2 106 M , similar to the dust mass of the Triangulum galaxy NGC 598 (M33). A further intercomparison of optical and ISO images reveals that the morphology of the warp of the central spiral may be optically traced: the contours of an entire one half of the spiral lie on the same warped ridge as that found in optical photographs.