First Results of the ISO Photometry of 12 μm Active Galaxies

Abstract

We present the preliminary results of the ISOPHOT survey of the active galaxies belonging to the 12μm galaxy sample. Most of the observations have been collected in an ISO open time programme, while others have been extracted from the ISO archive. We present new ISOPHOT photometry of 50 galaxies, and include the literature data of 21 other galaxies. The total sample is distributed roughly equally among the three classes of Seyfert 1s, Seyfert 2s and high luminosity non- Seyfert galaxies. The ISO photometry together with the IRAS data are used to define color-color diagrams and energy distributions. It appears that—on average - thermal dust emission at two temperatures (one cold at 15–30K and one warm at 50–70K) are su.cient to.t the 60–200μm energy distributions. The far-IR spectra of active galaxies, longward of 100μm, are dominated by thermal emission from dust in the host galaxies with a wide range of temperature, down to 15K. With the present data the contribution of the active nucleus or of a dusty torus around it cannot be disentangled from that of the host galaxies. Seyfert 1s appear to have the flatter 12–120μm spectrum, as already indicated by the IRAS data.

Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) with the participation of ISAS and NASA