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A Search for Low-Level Seyfert Activity in the 500 Brightest Northern Galaxies *

Published online by Cambridge University Press:  04 August 2017

Alexei V. Filippenko  and
Wallace L. W. Sargent
Alexei V. Filippenko
Affiliation:
Department of Astronomy, University of California, Berkeley, CA 94720 USA
Wallace L. W. Sargent
Affiliation:
Palomar Observatory, California Institute of Technology, Pasadena, CA 91125 USA

Abstract

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A sensitive search for intrinsically faint Seyfert nuclei in the 500 brightest northern galaxies is being conducted with the Hale 5.08 m telescope. The primary aim is to extend the luminosity function of active galactic nuclei (AGNs) to lower luminosities. Thus far, we have detected Hα emission having full-width near zero-intensity (FWZI) ≳ 4000 km s−1 in a significant fraction (≳10%) of nearby galaxies. Moreover, the narrow emission lines in a given nucleus often have markedly different widths, as shown in detail for M81. Those associated with high critical densities are generally the broadest, indicating that a very wide range of densities is present in the narrow-line region. The relative intensities of the lines can readily be explained with models in which clouds of gas having ne ≈ 102 to 107 cm−3 are photoionized by nonstellar radiation such as that produced by QSOs and luminous Seyfert 1 galaxies.

Type
VII. Low Level Activity and Intermediate Objects
Information
Symposium - International Astronomical Union , Volume 121: Observational Evidences of Activity of Galaxies , 1987 , pp. 451 - 460
Copyright
Copyright © Reidel 1987 

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