RADIAL VELOCITY OFFSETS DUE TO MASS OUTFLOWS AND EXTINCTION IN ACTIVE GALACTIC NUCLEI

Abstract

We present a study of the radial velocity offsets between narrow emission\nlines and host galaxy lines (stellar absorption and H I 21-cm emission) in\nSeyfert galaxies with observed redshifts less than 0.043. We find that 35% of\nthe Seyferts in the sample show [O III] emission lines with blueshifts with\nrespect to their host galaxies exceeding 50 km/s, whereas only 6% show\nredshifts this large, in qualitative agreement with most previous studies. We\nalso find that a greater percentage of Seyfert 1 galaxies show blueshifts than\nSeyfert 2 galaxies. Using HST/STIS spatially-resolved spectra of the Seyfert 2\ngalaxy NGC 1068 and the Seyfert 1 galaxy NGC 4151, we generate geometric models\nof their narrow-line regions (NLRs) and inner galactic disks, and show how\nthese models can explain the blueshifted [O III] emission lines in collapsed\nSTIS spectra of these two Seyferts. We conclude that the combination of mass\noutflow of ionized gas in the NLR and extinction by dust in the inner disk\n(primarily in the form of dust spirals) is primarily responsible for the\nvelocity offsets in Seyfert galaxies. More exotic explanations are not needed.\nWe discuss the implications of this result for the velocity offsets found in\nhigher redshift AGN.\n