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Published December 1, 1989 | Published + Erratum
Journal Article Open

Continuum energy distribution of quasars: Shapes and origins


Continuum observations from ~0.3 nm to 6 cm (10^(9.7)-10^(18) Hz) are presented for 109 bright quasars from the Palomar-Green (PG) survey. Two-thirds of the quasars have been detected in the infrared at wavelengths between 10 and 100 μm. All of the PG quasars appear to emit the bulk of their luminosity (typically more than 90%) between 3 nm and 300 μm (10^(12)-10^(17) Hz). The total luminosity at wavelengths longer than 1 μm is typically 20%-40% of that at wavelengths shortward of 1 μm. The gross shape of the energy distributions between 3 nm and 300 μm is remarkably similar for all the quasars except the flat-spectrum radio-loud quasars like 3C 273 and can plausibly be fitted by two broad components of thermal emission. In this interpretation the emission in the spectral range ~ 10 nm to 0.3 μm, the "big blue bump," is dominated by 10,00-100,000 K thermal emission from an accretion disk. The emission between 2 μm and 1 mm, the "infrared bump," is made up of reradiation from dust in a distorted disk extending from 0.1 pc to more than 1 kpc. The fairly small range in the relative sizes of the bumps suggests that the covering factor in most of the PG quasars is similar. There is no obvious connection between the strengths of the blue and infrared peaks and whether or not the quasar is radio quiet or radio loud. The mass of infrared emitting dust is estimated to be ~0.01 M_☉ at 2 μm and ~ 10^5 M_☉ at 60 μm. The radiation from 0.5 μm is thermal emission from the portion of the disk between 0.1 and 1 pc, illuminated primarily by the clouds of the broad-line region. The radiation from 5 μm to 1 mm is reradiation from a warped disk at distances greater than 1 pc from the central source, which is heated directly by radiation from the central source. Optically thin atomic emission (free-free and partially thermalized lines and bound-free) from gas within 1 pc of the central source, whose dust has sublimated, probably contributes to the flux from 0.5 to 2 μm. We believe that there is no convincing evidence for energetically significant nonthermal radiation in the wavelength range 3 nm to 300 μm in the continua of the radio-quiet and steep-spectrum radio-loud PG quasars.

Additional Information

© 1989 American Astronomical Society. Received 1989 February 2; accepted 1989 June 2 We thank Richard Green for providing us with the original data for the PG quasars and for helpful comments on the manuscript. We also thank our night assistants at Palomar, Juan Carasco and Skip Staples, for assistance in obtaining the infrared photometry. We acknowledge useful discussions with R. Blandford, and thank J. Bechtold and K. Kelleman for allowing us to use their data prior to publication. D. B. S., B. T. S., and G. X. N. are supported in part by the IRAS extended mission program. E. S. P. is supported in part by NSF PYI grant AST 84-51725 and the Irvine Foundation. Ground based infrared astronomy at Caltech is supported by a grant from the NSF.

Attached Files

Published - 1989ApJ___347___29S.pdf

Erratum - 1990ApJ___357__291S.pdf


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