Continuum radiation from active galactic nuclei

Sembay, Steven Frederick (1987) Continuum radiation from active galactic nuclei. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

The results of a study of the continuum energy distribution and temporal variability of a number of active galactic nuclei (AGN) are presented. Quasi-simultaneous multi-frequency observations of the Seyfert type 1 galaxies, MCG 8-11-11, MKN 79 and MKN 279 are presented. The overall energy distributions of these objects are similar and have spectra which peak in the far-infrared. We have fitted a standard synchrotron model to the spectrum of MKN 279 and find a lower limit on the size of the region emitting the infrared continuum of ∼ 8x10^15 cm. Many AGN, however, are thought to have infrared continua which are contaminated by thermal re-radiation by dust grains within the narrow-line region of these objects. We find some evidence to support this by showing that there is a correlation between the far-infrared luminosities of a sample of AGN with the narrow-line [0III]λ 5007+4959 luminosity. However, the correlation is not strong and may be affected by intrinsic variability of the normalizing factors (the H_α/ and H_β/ broad Balmer lines). We present far-infrared data on the radio-loud QSO 0241+62. Our data are consistent with a continuous radio to infrared spectrum although there is some slight evidence to suggest that the infrared continuum may peak at 25 μm. We also present quasi-simultaneous multi-frequency data on the blazar MKN 501. In this case, however, the overall spectrum is entirely consistent with the relativistic jet models that have been applied to the continua of blazars and which predict that the radio to ultraviolet continuum is continuous. One method of locating the continuum emission from a given waveband in AGN to a particular region is to measure the variability time-scale. We present a mid- to far-infrared variability study of a heterogeneous sample of nine active galaxies. None of the six Seyferts/low-luminosity QSOs in our sample showed any evidence for variability on the time-scales of the observations (generally weeks to months). However, only two of these objects, the Seyfert 2 galaxy NGC 1275 and the intermediate Seyfert 1.5 galaxy MKN 6, were sufficiently bright and observed often enough for their lack of variability to be definitely attributed to a strong contamination of their infrared continua by thermal dust emission. (D75979/87)

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