The ISOPHOT View of Quasars and Radiogalaxies

Abstract

We summarize the current status of the ISOPHOT Guaranteed Time Proposal on quasars and radio-galaxies. The ISO data from 4.8 to 200 μm, complemented by additional ground-based measurements at 1300 μm, yield spectral energy distributions that show two components of different strength: i) synchrotron emission that dominates the radio range and — depending on the spectral slope — may extend into the near infrared regime. ii) Thermal dust emission that dominates the infrared regime but may be masked — in extreme cases of flat spectrum radio quasars — by the synchrotron component. The spectralenergy distributions exhibit different shapes that reflect the various contributions of the AGN and the star formation to the heating of the dust in the nucleus and the outer parts of the host galaxy. The relative contributions of synchrotron and dust emission and the broad range of dust temperatures support a picture where the observational appearance of quasars and radio-galaxies is determined by the dust morphology (circum-nuclear torus/individual dust clouds) and by different viewing angles (beamed radio emission/ scattered blue emission) towards the source.