Observations and a model for the infrared continuum of Centaurus A

The definitive version is available at www.blackwell-synergy.com. Copyright Blackwell Publishing DOI : 10.1046/j.1365-8711.1999.02908.xWe present ISOPHOT S, ISOSWS and 8 to 13 mi- cron ground based observations of Centaurus A that show prominent PAH and silicate features. These and other data are used to construct a model for the infrared continuum. We find that in a nuclear sized aperture (~4 arcsec,~60 pc) the SED is characteris- tic of emission from a starburst and AGN torus; in larger apertures an additional component of cirrus emission is required. Based on our model, the torus diameter is estimated to be 3.6 pc and the best fit- ting inclination angle of the torus is 45 degrees. This result has implications for the detectability of tori in low power AGN and in particular for the use of the IRAS 60/25 micron flux ratio as an indicator of the torus inclination.Peer reviewe