Velocity Offsets Due to Mass Outflows in Active Galaxies

Abstract

Abstract. We present a study of the radial velocity offsets between AGN-related narrow emission lines and host-galaxy emission and absorption lines in Seyfert galaxies with observed redshifts less than 0.043. We find that 35% of the Seyferts in the sample show [O iii] emission lines with blueshifts with respect to their host galaxies exceeding 50 km s −1 , whereas only 6% show redshifts this large, in qualitative agreement with most previous studies. We also find that a greater percentage of Seyfert 1 galaxies show blueshifts than Seyfert 2 galaxies. Using HST/STIS spatially-resolved spectra of the Seyfert 2 galaxy NGC 1068 and the Seyfert 1 galaxy NGC 4151, we generate geometric models of their narrow-line regions (NLRs) and inner galactic disks and show how these models can explain the blueshifted [O iii] emission lines in collapsed STIS spectra of these two Seyferts. We conclude that the combination of mass outflow of ionized gas in the NLR and extinction by dust in the inner disk (primarily in the form of dust spirals) is primarily responsible for the velocity offsets in Seyfert galaxies.