Seyfert nuclei - of environments found for Seyferts,...

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Seyfert nuclei: Seyfert galaxies seem to have more companions than non-Seyferts of the same kind and luminosity (Dahari 1984 AJ 89, 966, MacKenty 1989 ApJ 343, 125), but the strength of this result depends critically on just how the control sample is selected (Fuentes-Williams and Stocke 1988 AJ 96, 1235). Samples of interacting galaxies are rich in Seyferts (Keel et al. 1985 AJ 90, 2208) but this survey plus those of Dahari 1985 (ApJ Suppl 57, 143) and Bushouse (1986 AJ 91, 255) also shows that very distorted galaxies almost never have Seyfert nuclei. The upshot is that perturbations make it easier to have Seyfert activity, but do not appear utterly essential (to first order, a bar acts like a small companion). When a Seyfert nucleus is present, it is usually in the brighter pair member, and preferentially in host galaxies with the most concentrated bulge masses as judged from rotation curves (Keel 1996 AJ AJ 111, 696). This panel shows the kinds
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Unformatted text preview: of environments found for Seyferts, including luminous companions and tidal tails. Radio galaxies: Radio galaxies are more likely to have close companions than optically similar radio-quiet galaxies (Heckman et al. 1985 ApJ 288, 122); note that here too the details of sample selection are rather important in one's result (Dressel 1981 ApJ 245, 25; Stocke 1978 AJ 83, 348; Adams et al. 1980 AJ 85, 1010). The highest-luminosity nearby radio galaxies almost universally show evidence of strong interactions or mergers (Heckman et al. 1986 ApJ 311, 586). Detailed studies of a few such cases show evidence that the galaxy recently acquired substantial gas (van Breugel et al. 1984 ApJ 277, 82; Heckman et al. 1982 ApJ 262, 529). This was suspected in the 1950s from Centaurus A. The HST snapshot survey of 3CR radio galaxies has shown a large fraction to show some kinds of morphological distortions (de Koff et al. 1996 ApJSuppl 107, 621)....
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