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A detailed study of the emission lines in the Seyfert 1 nucleus of M81
Filippenko, Alexei V.; Sargent, Wallace L. W.
AA(California, University, Berkeley), AB(Palomar Observatory, Pasadena)
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 324, Jan. 1, 1988, p. 134-153. Research supported by the University of California. (ApJ Homepage)
Publication Date:
NASA/STI Keywords:
Astronomical Spectroscopy, Emission Spectra, Galactic Nuclei, Line Spectra, Seyfert Galaxies, Visible Spectrum, Absorption Spectra, H Alpha Line, Signal To Noise Ratios, Spectral Resolution
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The authors present optical spectra of M81 having moderate resolution (1.6 - 4.5 Å) and exceptionally high signal-to-noise ratios. The broad component of Halpha emission first noticed by Peimbert and Torres-Peimbert is easily visible, confirming that M81 harbors an active galactic nucleus (AGN) of the Seyfert 1 type. Prominent forbidden lines are also present. An absorption-line template galaxy, NGC 4339, is used to eliminate the starlight, revealing the pure emission-line spectrum of M81. A detailed analysis of the nuclear narrow-line region is given. It is shown that a wide range of densities is present, making the observed relative intensities consistent with photoionization by dilute, nonstellar radiation. The authors derive the mass of the central object in M81 (≡5×105M_sun;), under the assumption that the widths of the broad permitted lines are induced by gravity. It appears that there have been no changes in the strength of the broad Halpha line during the past few years, even though the X-ray flux of M81 has been observed to vary substantially.

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