VTechWorks staff will be away for the Thanksgiving holiday beginning at noon on Wednesday, November 27, through Friday, November 29. We will resume normal operations on Monday, December 2. Thank you for your patience.

Browsing by Author "Mushotzky, R. F."

Now showing 1 - 2 of 2
  • Thumbnail Image
    Radial velocity offsets due to mass outflows and extinction in active galactic nuclei
    Crenshaw, D. M.; Schmitt, H. R.; Kraemer, S. B.; Mushotzky, R. F.; Dunn, Jay P. (IOP Publishing Ltd., 2010-01)
    We present a study of the radial velocity offsets between narrow emission lines and host galaxy lines (stellar absorption and Hi 21 cm emission) 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 Hubble Spce Talescope/Space Telescope Imaging Spectrograph 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. More exotic explanations are not needed. We discuss the implications of this result for the velocity offsets found in higher redshift active galactic nuclei.
  • Thumbnail Image
    Ultraviolet and X-ray Variability of the Seyfert 1.5 Galaxy Markarian 817
    Winter, L. M.; Danforth, C.; Vasudevan, R.; Brandt, W. N.; Scott, J.; Froning, C.; Keeney, B.; Shull, J. M.; Penton, S.; Mushotzky, R. F.; Schneider, D. P.; Arav, Nahum (IOP PUBLISHING LTD, 2011-02)
    We present an investigation of the ultraviolet and X-ray spectra of the Seyfert 1.5 galaxy Markarian 817. The ultraviolet analysis includes two recent observations taken with the Cosmic Origins Spectrograph (COS) in 2009 August and December, as well as archival spectra from the International Ultraviolet Explorer and the Hubble Space Telescope. Twelve Ly alpha absorption features are detected in the 1997 Goddard High Resolution Spectrograph (GHRS) and 2009 COS spectra-of these, four are associated with high-velocity clouds in the interstellar medium, four are at low significance, and the remaining four are intrinsic features, which vary between the GHRS and COS observations. The strongest intrinsic absorber in the 1997 spectrum has a systemic velocity of similar to-4250 km s(-1). The corresponding feature in the COS data is five times weaker than the GHRS absorber. The three additional weak (equivalent width from 13 to 54 m angstrom) intrinsic Lya absorbers are at systemic velocities of -4100 km s(-1), -3550 km s(-1), and -2600 km s(-1). However, intrinsic absorption troughs from highly ionized Civ and N v are not detected in the COS observations. No ionized absorption signatures are detected in the similar to 14 ks XMM-Newton EPIC spectra. The factor of five change in the intrinsic Lya absorber is most likely due to bulk motions in the absorber, since there is no drastic change in the UV luminosity of the source from the GHRS to the COS observations. In a study of the variability of Mrk 817, we find that the X-ray luminosity varies by a factor of similar to 40 over 20 years, while the UV continuum/emission lines vary by at most a factor of similar to 2.3 over 30 years. The variability of the X-ray luminosity is strongly correlated with the X-ray power-law index, but no correlation is found with the simultaneous optical/UV photometry.