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Effects of internal dust on the NLR Lyman and Balmer decrements

  • Binette, Luc
  • Wang, John
  • Villar-Martin, Montserrat
  • Martin, Peter G.
  • Magris C., Gladis
Publication Date
May 01, 1993
DOI: 10.1086/173101
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Detailed calculations on the effects of internal dust on the Balmer and Lyman decrements are presented for a spherically symmetric distribution of low covering factor clouds photoionized by a power law. Consideration is given to the important effects of perspective on the emergent fluxes, which in the present simplified scheme present either the photoionized face to the observer or the back face. For moderate amounts of internal dust, the relative internal dust content by mass (mu) is 0.2-0.3, radiation-bounded clouds result in Lyman and Balmer decrements in the range 32-37 and 3.0-3.1, respectively. Seyfert 2 observations show much lower Lyman decrements than predicted from the spherically symmetric model, and a critical study is made of various explanations. Attention is also given to the possibility that dust reddening of the continuum may account for the apparent deficit of ionizing photons seen in many Seyfert 2s. This reddening may be present in addition to, or in place of, the anisotropic beaming/occultation of ionized radiation that is generally invoked to explain the deficit.

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