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

We report on Mid-Infrared (MIR) observations of the Seyfert 2 galaxy NGC 1068, obtained with ISOCAM in low-resolution spectro-imaging mode. The spatial resolution (∼5′′) allows us to disentangle the circumnuclear starburst regions from the emission of the active galactic nucleus (AGN). The global spatial distribution of the Unidentified Infrared Bands (UIBs) is similar to the cold dust component, traced by the 450μm emission and the gaseous component obtained from the CO(1–0) map. However, a shift between the maximum of the UIB and 450μm emission is clearly seen in our maps. The UIBs in the MIR (5–16 μm) originate almost exclusively from the starburst regions in the galactic disk with an emission peaking at the extremity of the stellar/gaseous bar at a distance of 1 kpc from the AGN. The spectrum of the nucleus is characterized over the whole 5–16μm range by a strong continuum which can be fitted with a power law of index α = −1.7. Moreover, the high [NeIII]/[NeII] ratio (> ∼ 2.5) in the nuclear region argues for a hard radiation field from the AGN. Observations indicate that the AGN in NGC 1068 contributes less than ∼5% to the total integrated UIB emission even though its hot dust continuum contributes as much as 75% to the total MIR flux. On the contrary, the nuclear contribution to the cold dust emission decreases considerably at submillimeter wavelengths and does not represent more than 25% of the total integrated emission at 450μm.

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