Broadband Properties of Active Galactic Nuclei

Citation

Edelson, Richard Allen (1987) Broadband Properties of Active Galactic Nuclei. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/gtk1-3n45. https://resolver.caltech.edu/CaltechETD:etd-09092008-113501

Abstract

The broadband radio-infrared-optical-ultraviolet properties of active galactic nuclei are used to investigate the nature of the central engine and the surrounding environment. Optically selected quasars (which have α̅_IR = -1.09; S_ν ∝ ν^α) and Seyfert 1 galaxies (α̅_IR = -1.15) tend to have relatively flat infrared spectra and low reddenings, while most Seyfert 2 galaxies (α̅_IR = -1.56) and other dusty objects have steep infrared spectra and larger reddenings. The infrared spectra of most luminous radio-quiet active galaxies turn over near ~80 µm. It appears that the infrared spectra of most quasars and luminous Seyfert 1 galaxies are dominated by unreprocessed radiation from a synchrotron self-absorbed source of order a light day across, about the size of the hypothesized accretion disk. Seyfert 2 galaxies and other reddened objects have infrared spectra which appear to be dominated by thermal emission from warm (~50 K) dust, probably in the disk of the underlying galaxy. A broad emission feature, centered near 5 µm, is present in many luminous quasars and Seyfert 1 galaxies.

Highly polarized objects ("blazars") can be strongly variable at far-infrared wavelengths over time scales of months. There is no conclusive evidence for far-infrared variations in normal (low-polarization) quasars or Seyfert galaxies, although low-level flickering (at the ~30% peak-to-peak level) cannot be ruled out.

Seyfert galaxies tend to have steep radio spectra (α_rad ≈ -0.7). The radio spectra of Seyfert 1 galaxies often flatten out near 2 cm. There is no significant difference in the mean radio luminosities of Seyfert 1 and 2 galaxies. There are of order 10⁵ Seyfert galaxies/Gpc³, most of which have 6 cm luminosities between 10^37.0 and 10^39.4 ergs/s and 60 µm luminosities between 10^42.2 and 10^45.0 ergs/s. The Seyfert 2 galaxy radio luminosity function cuts off sharply below 10^37.4 ergs/s.

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