Broadband Properties of Active Galactic Nuclei

Author: Edelson, Richard Allen

Year: 1987

Degree: Dissertation (Ph.D.)

Advisor: Schmidt, Maarten

Committee Members: Schmidt, Maarten; Moffet, Alan Theodore; Scoville, Nicholas Zabriskie; Readhead, Anthony C. S.; Blandford, Roger D.

Option: Astronomy

DOI: 10.7907/gtk1-3n45

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 α̅IR = -1.09; Sν ∝ να) and Seyfert 1 galaxies (α̅IR = -1.15) tend to have relatively flat infrared spectra and low reddenings, while most Seyfert 2 galaxies (α̅IR = -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 (αrad ≈ -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 1037.0 and 1039.4 ergs/s and 60 µm luminosities between 1042.2 and 1045.0 ergs/s. The Seyfert 2 galaxy radio luminosity function cuts off sharply below 1037.4 ergs/s.

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