Far Ultraviolet Spectroscopic Explorer Observations of the Seyfert 1 . 5 Galaxy NGC 5548 in a Low State

We present far-ultraviolet spectra of the Seyfert 1.5 galaxy NGC 5548 obtained in 2000 June with the Far Ultraviolet Spectroscopic Explorer (FUSE). Our data span the observed wavelength range 915–1185 Å at a resolution of ∼ 20 km s. The spectrum shows a weak continuum and emission from O VI λλ1032,1038, C III λ977, and He II λ1085. The FUSE data were obtained when the AGN was in a low state, which has revealed strong, narrow O VI emission lines. We also resolve intrinsic, associated absorption lines of O VI and the Lyman series. Several distinct kinematic components are present, spanning a velocity range of ∼ 0 to − 1300 km s relative to systemic, with kinematic structure similar to that seen in previous observations of longer wavelength ultraviolet (UV) lines. We explore the relationships between the far-UV absorbers and those seen previously in the UV and X-rays. We find that the high-velocity UV absorption component is consistent with being low-ionization, contrary to some previous claims, and is consistent with its non-detection in high-resolution X-ray spectra. The intermediate velocity absorbers, at −300 to − 400 km s, show H I and O VI column densities consistent with having contributions from both a high-ionization X-ray absorber and a low-ionization UV absorber. No single far-UV absorbing component can be solely identified with the X-ray absorber. Kitt Peak National Observatory, National Optical Astronomy Observatories, P.O. Box 26732, 950 North Cherry Ave., Tucson, AZ, 85726-6732; mbrother, [email protected] Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 Center for Astrophysical Sciences, Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD 21218–2686 Laboratory for Astronomy and Solar Physics, Code 681, NASA/Goddard Space Flight Center, Greenbelt, MD 20771 Herzberg Institute of Astrophysics, National Research Council of Canada, Victoria, BC, V9E 2E7, Canada; [email protected]