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Many quasars and active galactic nuclei show a bump or excess in the near-infrared continuum. In this paper, a model is developed to account for the bump in terms of thermal radiation from dust heated by the primary optical/ultraviolet continuum source. This model naturally explains the onset of the bump at about 2 μm, since this wavelength corresponds to the spectral peak for optically thin emission from graphite grains at their evaporation temperature (≡1500K). Infrared spectra are calculated for two cases, one in which the grains are smoothly distributed and another in which the dust is clumped into discrete clouds that are optically thick to the ultraviolet continuum. Continuum spectra of 3C 273 and the "infrared quasar" IRAS 13349+2438 are fitted between ≡0.1 and 100 μm with a multicomponent model.
Richard Barvainis (Tue,) studied this question.