The relative frequency of broad-lined and narrow-lined active galactic nuclei - Implications for unified schemes

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

Evidence concerning the relative occurrence of narrow-lined and broad-lined AGN in optical, IR, X-ray, and radio-selected samples are discussed. Marginal evidence that narrow-lined AGN were more common in the past is found. Narrow-lined objects have weaker O III forbidden lines at a given radio power. These data are inconsistent with the simplest 'unified scheme', where a similar thick molecular torus surrounds all AGN, and with the simplest modification, that torus geometrical thickness is a function of source power. It is argued that both the typical geometrical thickness and the typical optical thickness of obscuring material vary with source power. It is proposed that the obscuring material, rather than being an orbiting torus of cool molecular matter, may be an expelled shell of gas, only the outer parts of which are dusty.
Original languageEnglish
Pages (from-to)586-592
JournalMonthly Notices of the Royal Astronomical Society
Volume252
DOIs
Publication statusPublished - 15 Oct 1991

Keywords / Materials (for Non-textual outputs)

  • Active Galactic Nuclei
  • Radio Astronomy
  • Seyfert Galaxies
  • Spectral Line Width
  • Cosmic Dust
  • Forbidden Bands
  • Optical Thickness

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