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

Abstract

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-15mu m 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 \cite{quillen93} and find a striking correspondence with the ridges seen in emission 15 mu m 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-15{mu m} map, we derive a dust mass of approximately 2 10⁶ M_sun, 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. Based on data obtained with ISO, an ESA project with instruments funded by the ESA member states (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) with the participation of ISAS and NASA.