Computer Science
Scientific paper
Aug 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007phdt........20d&link_type=abstract
Proquest Dissertations And Theses 2007. Section 0079, Part 0606 183 pages; [Ph.D. dissertation].United States -- Georgia: Georg
Computer Science
Seyfert Galaxies, Active Galaxies, Quasars, Ultraviolet Absorption, Absorption Lines
Scientific paper
We present a survey of 72 Seyfert galaxies and quasars observed by the Far Ultraviolet Spectroscopic Explorer (FUSE). Our survey is the largest to date searching for intrinsic UV absorption with high spectral resolution, and is the first step toward a more comprehensive study of intrinsic absorption in low- redshift AGN. We have determined that 72 of 253 available active galactic nuclei (AGN) are viable targets for detection of intrinsic absorption lines. We examined these spectra for signs of intrinsic absorption in the O VI doublet (ll1031.9, 1037.6) and Lyman b (l1025.7). The fraction of Seyfert 1 galaxies and low-redshift quasars at z [Special characters omitted.] 0.15 that show evidence of intrinsic UV absorption is ~50%, which is slightly lower than Crenshaw et al. found (60%) based on a smaller sample of C IV absorption in Seyfert 1 galaxies observed with the Hubble Space Telescope (HST). The intrinsic absorption lines are mostly blueshifted with respect to the rest frame of the galaxy, indicating outflow of ionized gas from the AGN. With this new fraction we find a global covering factor of the absorbing gas with respect to the central nucleus of ~0.4.
We also provide a deeper analysis of the intrinsic absorption features we found in 35 objects. We have characterized the relation between luminosity and velocity, and examined the relationships between equivalent width, full width at half maximum, velocity and continuum flux. The luminosity/velocity correlation has been explored previously by Laor & Brandt (2002), but at a significantly higher redshift and heavily weighted by Broad Absorption Line quasars. Our survey is for lower redshift and lower luminosity objects, mostly Seyfert galaxies.
We have also explored each object with multiple observations for variablity in each of the aforementioned quantities and characterized the variation of equivalent width with continuum flux. Variability for low-z AGN has been seen in the past. In our survey, we find that variability of O VI (ll1032, 1038) is less common than for the UV doublets of C IV and N V seen at longer wavelengths, because the O VI absorption is usually saturated. Lyman b absorption variability is more frequent. In the target-by-target examination we find that Broad Absorption Line (BAL) features and Narrow Absorption Line (NAL) features are related, in that they follow a single relationship between the maximum outflow velocity and the AGN luminosity, and both can be exhibited in similar luminosity objects.
IRAS F22456-5125 is one particular Seyfert galaxy that we have selected for modelling due to its interesting assortment of intrinsic absorption lines. It shows a system of five individual kinematic components of absorption features in both O VI lines and in several of the Lyman series lines. We find that each of the components are relatively simple to model and appear to be weak in the X-ray.
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