Broadband Properties of Active Galactic Nuclei

• Main Author: Edelson, Richard Allen
• Format: Others
• Language: en
• Published: 1987
• Online Access: https://thesis.library.caltech.edu/3413/1/Edelson_r_1987.pdf; 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 <https://resolver.caltech.edu/CaltechETD:etd-09092008-113501>

<p>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 <i>α&#773;_IR</i> = -1.09; <i>S_ν</i> ∝ ν^α) and Seyfert 1 galaxies (<i>α&#773;_IR</i> = -1.15) tend to have relatively flat infrared spectra and low reddenings, while most Seyfert 2 galaxies (<i>α&#773;_IR</i> = -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 <i>µ</i>m. 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 <i>µ</i>m, is present in many luminous quasars and Seyfert 1 galaxies.</p> <p>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.</p> <p>Seyfert galaxies tend to have steep radio spectra (<i>α_rad</i> ≈ -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 <i>µ</i>m 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.</p>