Dusty Disks and the Infrared Emission from AGN
The distortions inferred in the gaseous disks of active galaxies suggest that a significant, and possibly dominant fraction of the 1 - 1000μm radiation observed from AGN must be thermal emission from gas and dust heated by the central source. We report calculations of the growth and sublimation of dust grains in the outer parts of accretion disks appropriate to AGN. The thermal state of the gas undergoes a sudden change at the radius where the dust sublimates. The outer portion of the accretion disk radiates at 0.5 – 5 μm; free-free emission from gas whose dust has sublimated contributes to the flux at 0.5 – 2μm. If this thermal emission dominates the flux from radio-quiet quasars, it naturally explains the frequency and depth of the universal minimum in νF ν at 1014.5 Hz. Free-free emission from the photoionized surface layers of the disk at larger radii produces a radio flux at ν ≲ 1011 HZ comparable to that observed in radio-quiet quasars. The far-infrared and submillimeter emission from radio-quiet quasars and Seyfert galaxies is more naturally interpreted as reradiation by dust, than as nonthermal emission from the inner accretion disk.
KeywordsAccretion Disk Column Density Covering Factor Infrared Emission Central Source
Unable to display preview. Download preview PDF.
- Gunn, J.E. 1979 in Active Galactic Nuclei, eds. C. Hazard and S. Mitton, (Cambridge: Cambridge U. Pr.), 213.Google Scholar
- Haniff, C.A., Wilson, A.S., and Ward, M.J. 1988 Preprint.Google Scholar
- Kelley, K.K. 1973 In Selected Values of Thermodynamic Properties of the Elements, Am. Soc. Metals, Metals Park, pp. 87 ff.Google Scholar
- MacAlpine, G.M. 1985 in Astrophysics of Active Galactic Nuclei, ed. J.S. Miller (Mill Valley: Univ. Science Books), 259.Google Scholar
- MacKenty, J.W., and Stockton, A. 1984 Ap. J., 327, 116.Google Scholar
- Martin, P.G. 1978 Cosmic Dust, Oxford: Clarendon Press.Google Scholar
- Moorwood, A.F.M. 1989 in Infrared Spectroscopy in Astronomy, ESA SP-290, eds. A.C.H. Glasse, M.F. Kessler, and R. Gonzalez-Riesta.Google Scholar
- Reif, F. 1965 Fundamentals of Statistical and Thermal Physics, (New York: McGraw-Hill).Google Scholar
- Sanders, D.B, Phinney, E.S., Neugebauer, G., Soifer, B. T., and Matthews, K. 1989 Ap. J. in press.Google Scholar
- Scheuer, P.A.G. 1987 in Superluminal Radio Sources, eds. J.A. Zensus and T.J. Pearson (Cambridge: Cambridge U. Pr.), 104.Google Scholar
- Whittet, D.C.B. 1988 in Dust in the Universe, eds. M.E. Bailey and D.A. Williams, (Cambridge: Cambridge U. Pr.) 25.Google Scholar