A statistical study of companions to Seyfert galaxies

Whether Seyfert galaxies possess an excess of close companion galaxies is investigated using a large sample of nearby Seyferts and a control sample of "normal" spirals. The control sample has been carefully chosen to match the Seyfert sample in all respects except nuclear activity. Background subtraction is accomplished by considering only those galaxies that would be in the most probable range of absolute luminosities if they were companions to the Seyfert (i.e., near the "knee" of the luminosity function). Unlike the previous study by Dahari (1984), we find only very marginal evidence that Seyferts possess an excess of comparably sized companions. However, based upon the strength of Dahari's earlier positive result, the current dataset was reconsidered seeking a resolution between the two studies. A partial resolution is possible if the excess of companions near Seyferts is primarily due to low-luminosity galaxies (M_v_ >= -18) that would have been eliminated as background by our original technique. Further tests using both datasets strongly support the result that while Seyferts have only a marginal excess of bright companions, they possess a clear excess of faint companions, although the excess found is not nearly so large as that found in the Dahari study. The environment of Seyferts is also compared to that of radio galaxies; Seyferts are found to be in sparser environments than either type of radio galaxy, those with strong emission lines in their nuclear spectra (qualitatively similar to the nuclear spectra of Seyferts), and those without strong emission lines.