THE CONTINUUM INFRARED-EMISSION OF AGN

Far-infrared observations, obtained with the Infrared Astronomical Sat ellite, have shown intense IR emission in AGNs. Analyzing a sample com posed of Seyfert 2 galaxies, narrow-line radio galaxies and low ioniza tion nuclear emission-line regions (LINERs), we show that the IR conti nua of these objects are not significantly contamined by the emission lines, in contrast with planetary nebulae and H II regions. Studying t he IR continua of Sy 2, and determining their thermal and nonthermal c omponents, we conclude that the IR emission is mainly due to thermal r eradiation by dust heated by the central source, and distributed in th e narrow-line region (NLR) with an estimated mass of the order of 20-8 0 M.. Furthermore, comparing the relative IRAS fluxes of these AGNs, i ncluding starburst galaxies (SBG), we found that Sy 2 have the most lu minous IR nuclei, followed by NLRGs, SBGs, and LINERs. This sequence c an be understood on the basis of the importance of the dust contributi on to the IR continuum of each object.