THE CONTINUUM INFRARED EMISSION OF AGN

Far-infrared observations, obtained with the Infrared Astronomical Satellite, have shown intense IR emission in AGNs. Analyzing a sample composed of Seyfert 2 galaxies, narrow-line radio galaxies and LINERs (Low Ionization Emission-line Region), we show that the IR continua of these objects are not significantly contaminated by the emission lines, in contrast with planetary nebulae and H II regions. Studying the IR continua of Sy 2, and determining their thermal and non-thermal components, we conclude that the IR emission is mainly due to thermal reradiation by dust heated by the central source, and distributed in the narrow line region (NLR) with an estimated mass of the order of 20 to 80 solar mass. Furthermore, comparing the relative IRAS fluxes of these AGN, including starburst galaxies (SBG), we found that Sy 2 have the most luminous IR nuclei, followed by NLRG, SBG and LINERs. This sequence can be understood on the basis of the importance of the dust contribution to the IR-continuum of each object.