Comptonization effects as a test for hot intercloud medium in the broad-line region of active galactic nuclei

Abstract In the framework of the standard model for the BLR, we tackle the problem of testing the existence of a hot intercloud medium, required for the BLR cloud confinement. This is accomplished by analyzing the possible effects on broad-line profiles, specifically on Ly-alpha and H-alpha as representative of the two main classes of HILs and LILs. The presence of the hot gas has two major effects, namely Comptonization of the line photons and production of a diffuse field, illuminating the face of the clouds opposite to the central source; an analytical self-similar expression for the diffuse field has been obtained. Monte Carlo simulations have been used in order to derive the resulting profiles, which have been subsequently analyzed in terms of a parameterization scheme also suitable for observational tests. The main results concern distortions in the profiles, affecting the symmetry properties and relative shifts of the lines, and the formation of very extended wings, superposed on the underlying continuum.