ISO-SWS Observations of NGC 1068

Abstract

We present a first analysis of 2.4-45µm spectra of NGC 1068 obtained with the Short Wavelength Spectrometer SWS on board the Infrared Space Observatory ISO. The measured fine-structure line fluxes can be fit successfully by a simple photoionization model invoking an EUV bump in the ionizing continuum, similar to the case of the Circinus galaxy. Difference are observed between the [OIV] 26µm NLR line profile and optical NLR line profiles which may indicate significant extinction to part of the NLR. We detect pure rotational transitions of molecular hydrogen that must be emitted by molecular gas spanning a wide range of temperatures. The unusual strength of the fundamental S(0) 28µm rotational transition is evidence for a large (> 1.5 × 109 M⊙) gas mass at temperatures nea r 100 K. Either most of the gas in the circumnuclear region of NGC 1068 is warm or previous molecular mass estimates based on CO observations were too low. Strong mid-infrared continuum from the circumnuclear warm dust is prominent in our spectrum. The weak PAH emission detected at the edges of the 9.7µm silicate absorption should be considered in interpretations of the silicate feature.