Mid-infrared observations of NGC 1068 with the Infrared Space Observatory

We report on Mid-Infrared (MIR) observations of the Seyfert 2 galaxy NGC 10 68, obtained with ISOCAM in low-resolution spectro-imaging mode. The spatia l resolution (similar to5 ") allows us to disentangle the circumnuclear sta rburst regions from the emission of the active galactic nucleus (AGN). The global spatial distribution of the Unidentified Infrared Bands (UIBs) is si milar to the cold dust component, traced by the 450 mum emission and the ga seous component obtained from the (CO)-C-12(1-0) map. However, a shift betw een the maximum of the UIB and 450 mum emission is clearly seen in our maps . Thr UIBs ill the MIR (5-16 mum) originate almost exclusively from the sta rburst regions in the galactic disk with an emission peaking at the extremi ty of the stellar/gaseous bar at a distance of 1 kpc from the AGN. The spec trum of the nucleus is characterized over the whole 5-16 mum range by a str ong continuum which carl be fitted with a power lan of index alpha = -1.7. Moreover, the high [NeIII]/[NEII] ratio (greater than or similar to 2.5) in the nuclear region argues for a hard radiation held front the AGN. Observa tions indicate that the AGN in NGC 1068 contributes less than similar to5% to the total integrated UIB emission even though its hut dust continuum con tributes as much as 75% to the total MIR flux. On the contrary., the nuclea r contribution to the cold dust emission decreases considerably at submilli meter wavelengths and does not represent more than 2.5% of the total integr ated emission at 450 mum.