NEW CONSTRAINTS ON THE UNIFIED MODEL OF SEYFERT-GALAXIES

We present new 10 mu m (N-band) photometry for 70 Seyfert galaxies, 43 of them previously unobserved. These observations, together with thos e collected from the literature, complete the 10 mu m photometry for t he CfA Sy galaxies and cover 80% of the Sy found in the RSA and 70% of the Sy in the IRAS 12 mu m sample. From this data set, we find that S y not showing any evidence for broad lines are systematically weaker i n 10 mu m nuclear emission than Sy nuclei having broad lines. This res ult may indicate the existence of a group of very low-luminosity Sy2 g alaxies that do not have Sy1 counterparts in equal numbers, contrary t o the strict unified theory. Alternately, the result can be reconciled with unified theories if a specific type of geometry is assumed for t he circumnuclear obscuring material. By comparing the 10 mu m ground-b ased observations with the IRAS 12 mu m fluxes, we also study the prop erties of the extended mid-IR emission, i.e., the star forming activit y of the host galaxy of the Sy nucleus. We find Sy2 to lie preferentia lly in galaxies experiencing enhanced star-forming activity, while Sy1 lie in normal or quiescent galaxies. This result appears to be incons istent with the strict unified model, since the host galaxy properties should be independent of the orientation of a circumnuclear torus and therefore should be independent of nuclear type. Our finding could be explained by adding to the unified model a link between star-forming activity and the amount of obscuring material collected in the circumn uclear region.