21 research outputs found
Wiener Criteria for Existence of Large Solutions of Quasilinear Elliptic Equations with Absorption
The Properties of âDwarfâ Seyfert Nuclei in Nearby Galaxies
Accurate knowledge of the luminosity function of active galactic nuclei over a wide range of absolute magnitudes is a prerequisite to understanding their structure and evolution. Here we describe preliminary results from a large survey of bright, nearby galaxies which is designed to quantify the faint end of the luminosity function. Many high-quality spectra are shown to emphasize the great variety of physical conditions in the nuclei and to illustrate the methods used in a detailed analysis of the data. The characteristics of Seyfert galaxies are detected in a surprisingly large number of objects, although at much fainter levels than usually reported for classical AGNs. In particular, broad Hα emission is visible in at least 10% of the nuclei, and the relative intensities of narrow lines are often indicative of photoionization by a nonstellar continuum. A very wide range of densities is found in the narrow-line regions of certain low-ionization nuclei, just as in many QSOs and Seyfert 1 galaxies. These results suggest that intrinsically faint (âdwarfâ), but nevertheless active, nuclei are much more common than previously believed, and that they may have evolved from luminous quasars