## 5. Discussion and conclusionsThe interior of galactic nuclei is usually hidden to optical and near IR observers by a dust veil of high optical depth. Measurements in the far IR, which are not handicapped by obscuration, are until now always of low resolution and furthermore cannot detect stars directly. If one wishes to determine the spatial configuration of stars and dust in a galactic core, one has to use indirect means. One way is to model the observed IR energy distribution. If one succeeds in building a model that correctly reproduces the IR fluxes of a sufficiently large data base, one has, if not a true, but at least a self-consistent picture. If furthermore maps or observations of different spatial resolution indicate that spherical symmetry is not gravely violated, one has even derived the likely structure of the nucleus. The data of the four galaxies for which we computed models are
certainly not extensive, neither in spatial nor spectral resolution,
and are therefore only a first step towards the goal. Nevertheless,
the parameters in Table 2 give a first tentative description of
the nuclei. Of course, because of the simplified geometry and the
small number of parameters, one has to be skeptical about the
uniqueness of the models. For example, one may wonder why the transfer
code yields such a good fit to Arp 220. In the calculations, it was
assumed that the OB star density is constant over a galactic radius of
350 pc, whereas one sees at 2.2 So the method of deriving the structure of an obscured galactic nucleus from modeling its observed IR emission by computing the radiative transfer is cheap and promising, if one does not forget its limitations. © European Southern Observatory (ESO) 1999 Online publication: November 2, 1999 |