The ultraviolet spectrum of the Seyfert galaxies NGC 3516 and NGC 5548.

Abstract

The observation of the UV spectrum of Seyfert nuclei has made it possible to conduct a comparison of the UV spectra of active nuclei over a wide range of absolute luminosities. In a study of the two Seyfert galaxies NGC 3516 and NGC 5548 with the International Ultraviolet Explorer (IUE) satellite, Boggess et al. (1978) have found that remarkable variations of the continuum and of the profiles and intensities of the lines occurred in the UV spectrum of NGC 3516. The present investigation is concerned with observations of the nucleus of NGC 3516 and NGC 5548 with IUE in the low-dispersion mode at a resolution of 8 A and with a large aperture to ensure photometric accuracy. It was found that in both galaxies the UV continuum becomes harder when it brightens. In NGC 5548, for which the reddening is very small, the continuum variations suggest that the continuum is the sum of two components with different slopes. For NGC 3516 no conclusion can be reached as to whether a two-component would be appropriate.