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For refcode 1998ApJ...506..647S:
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1998ApJ...506..647S The Difference between the Narrow-Line Regions of Seyfert 1 and Seyfert 2 Galaxies HENRIQUE R. SCHMITT Departmento Astronomia, IF-Universidade Federal do Rio Grande do Sul, CP 15051, CEP 91501-970, Porto Alegre, RS, Brazil; schmitt@if1.if.ufrgs.br Received 1997 August 25; accepted 1998 June 1 ABSTRACT This paper presents a comparative study of emission-line ratios of the narrow-line regions (NLRs) of Seyfert 1 and Seyfert 2 galaxies. It includes a literature compilation of the emission-line fluxes [O II] {lambda}3727, [Ne III] {lambda}3869, [O III] {lambda}5007, and [Ne V] {lambda}3426 as well as 60 microns continuum flux, for a sample of 52 Seyfert 1 and 68 Seyfert 2 galaxies. The distribution of the emission-line ratios [O II]/[Ne III] and [O II]/[Ne V] shows that Seyfert 1 and Seyfert 2 galaxies are statistically different: Seyfert 1 galaxies have smaller values than Seyfert 2 galaxies, indicating a higher excitation spectrum. These and other emission-line ratios are compared with sequences of models that combine different proportions of matter and ionization-bounded clouds and also with sequences of models that vary only the ionization parameter. This comparison shows that the former models better reproduce the overall distribution of emission-line ratios, indicating that Seyfert 1 galaxies have a smaller number of ionization-bounded clouds than Seyfert 2 galaxies. This difference, together with other results available in the literature, are interpreted from the point of view of four different scenarios. The most likely scenario assumes that Seyfert 1 galaxies have smaller NLRs than Seyfert 2 galaxies, possibly due to a preferential alignment of the torus axis close to the host galaxy plane axis in Seyfert 1 galaxies. Subject headings: galaxies: Seyfert-galaxies: active-galaxies: nuclei
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