The IR Spectral Energy Distribution

The surprising fact is that nearly all of the dust in this QSO is at the sublimation temperature, T 1800K. This is indicated by the SED peak at around 2-3 m, and sharp decrease towards longer wavelengths (see Agol et al. 2001). There are a handful of other QSOs which show infrared bumps around the same wavelength (Wills 1987); however, in larger samples they appear to be quite rare (Edelson & Malkan 1986, Sanders et al. 1989). The infrared spectrum can be fit with a thin (i.e. dense) shell of dust with the temperature as a function of radius determined by reradiation of the QSO light (which may be absorbed by dust further in). The inner radius, R_in is set by the sublimation temperature, while radius at which an optical depth of 3 is reached is at

R_out = 3 R_in. The covering factor is about . Extrapolated to longer wavelength, the dust spectrum falls well below the millimeter upper limits (Agol et al. 2001).

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