The extended narrow line region of NGC 4151. I. Emission line ratios and their implications

• The paper presents the first results from long-slit spectra of the Seyfert galaxy NGC 4151 which give average diagnostic ratios of weak lines in the extended narrow line region (ENLR) of that galaxy and the first direct density measurement in an ENLR. These data confirm that the ENLR is kinematically undisturbed gas in the disc of the galaxy which is illuminated by an ionizing continuum stronger by a factor of 13 than a power law interpolated between observed ultraviolet and X-ray fluxes. Explanations of this apparent excess include a hot thermal continuum, time variations and an anisotropic radiation field. The authors give reasons for favouring anisotropy which might be caused by shadowing by a thick accretion disc or by relativistic beaming. Shadowing by a molecular torus is unlikely, given the absence of an infrared signal from the reradiated flux absorbed by any torus. Anisotropy would have important implications for the bolometric luminosity and nature of active galactic nuclei

Subject headings

NATURVETENSKAP  -- Fysik -- Astronomi, astrofysik och kosmologi (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Astronomy, Astrophysics and Cosmology (hsv//eng)

Keyword

Experimental/ astronomical spectra

galactic nuclei

interstellar matter

Seyfert galaxies

visible astronomical observations/ AD 1989 05 05 to 06

interstellar medium

extended narrow line region

NGC 4151

spectra

Seyfert galaxy

density

kinematically undisturbed gas

hot thermal continuum

time variations

anisotropic radiation field

shadowing

thick accretion disc

relativistic beaming

bolometric luminosity

active galactic nuclei

315 to 695 nm/ A9850R Active and peculiar galaxies A9850E Galactic structure

content and morphology A9840B Interstellar matter A9580J Photographic region astronomical observations/ wavelength 3.15E-07 to 6.95E-07 m

Publication and Content Type

ref (subject category)

art (subject category)