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Broadband Properties of Active Galactic Nuclei


Edelson, Richard Allen (1987) Broadband Properties of Active Galactic Nuclei. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/gtk1-3n45.


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.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Astronomy
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Astronomy
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Schmidt, Maarten
Group:Astronomy Department
Thesis Committee:
  • Schmidt, Maarten (chair)
  • Moffet, Alan Theodore
  • Scoville, Nicholas Zabriskie
  • Readhead, Anthony C. S.
  • Blandford, Roger D.
Defense Date:12 November 1986
Funding AgencyGrant Number
Record Number:CaltechETD:etd-09092008-113501
Persistent URL:
Related URLs:
URLURL TypeDescription adapted for Chapter Two. adapted for Chapter Three. adapted for Chapter Four. adapted for Chapter Five.
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:3413
Deposited By: Imported from ETD-db
Deposited On:17 Sep 2008
Last Modified:05 Nov 2021 23:00

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PDF (Edelson_r_1987.pdf) - Final Version
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