Starburst nuclei : ISO observations and models ?

1.) We present photometric data of three starburst galaxies (Mkn 496, Mkn 1116, NGC 6000) obtained with the Infrared Space Observatory (ISO) in the wavelength bands 2.5– 11.6 μm (P-40) and 120–200 μm (P-22). In all galaxies, we detect the 9.7 μm silicate absorption feature and strong emission from PAHs; only the 3.3 μm band is below the sensitivity limit of the instrument. 2.) We model the starbursts by computing the radiative transfer in the galactic nuclei under the assumption of spherical symmetry. By properly adjusting the distribution of stars and dust, we can fit the observed infrared radiation, including the PAH features. The dust is described by a mixture of large grains, very small grains and PAHs, the latter all of the same size (25 carbon atoms). The photo–destruction of the PAHs is computed in a physically consistent way. 3.) We explore the parameter space by modeling the spectral energy distribution of the ultraluminous starburst galaxy Arp 220. Although the nucleus is deeply hidden by dust, the simple radiative transfer calculations allow an estimate of its global structure.