Dense, thin clouds and reprocessed radiation in the central regions of active galactic nuclei

The primary radiation generated in the central continuum-forming region ofActive Galactic Nuclei can be reprocessed by very dense, small-scale cloudsthat are optically-thin to Thomson scattering. In spite of the extremeconditions expected to prevail in this innermost, central environment, theradiative clouds can survive and maintain cool temperatures relative to theambient emitting region by means of magnetic confinement. Motivated by theseideas, we present a detailed quantitative study of such clouds, explicitlydescribing the physical properties they can attain under thermal and radiativeequilibrium conditions. We also discuss the thermal stability of the gas incomparison to that of other reprocessing material thought to reside at largerdistances from the central source. We construct a model to predict the emergentspectra from a source region containing dense clouds which absorb and reemitthe primary radiation generated therein. Our predicted spectra show thefollowing two important results: (i) the reprocessed flux emitted at optical/UVenergies is insufficient to account for the blue bump component in the observedspectra; and (ii) the amount of line radiation that is emitted is at leastcomparable to (and in many cases dominates) the continuum radiation. The linesare extremely broad and tend to accumulate in the extreme ultraviolet, wherethey form a peak much more prominent than that which is observed in theoptical/UV. This result is supported by current observations, which indicatethat the spectral energy distribution of radio-quiet AGN may indeed reach amaximum in the EUV band.Comment: 14 pages, 5 figures, latex, uses epsf and rotate, accepted for publication in M