AAS 201st Meeting, January, 2003
Session 11. Seyfert Galaxies and AGNs
Poster, Monday, January 6, 2003, 9:20am-6:30pm, Exhibit Hall AB

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[11.06] Simultaneous UV and X-ray Spectroscopy of the Seyfert 1 Galaxy NGC 5548. I. Evidence for Dust in the UV Absorbers

S.B. Kraemer (CUA/NASA's GSFC), D.M. Crenshaw (Georgia State University), J.R. Gabel (CUA), J.S. Kaastra, K. Steenbrugge (SRON), I.M. George, T.J. Turner (UMBC/NASA's GSFC), T. Yaqoob (Johns Hopkins University), J.P. Dunn (Georgia State University)

We present new UV spectra of the nucleus of the Seyfert 1 galaxy NGC~5548, obtained with the Space Telescope Imaging Spectrograph at high spectral resolution (\lambda/\Delta\lambda = 30,000 - 46,000), simultaneously with Chandra X-ray Observatory spectra. Taking advantage of the low UV continuum and broad emission-line fluxes, we have determined that the deepest UV absorption component covers at least a portion of the inner high-ionization narrow-line region (NLR). Assuming the NLR is fully covered, we find nonunity covering factors in the cores of several components, which increase the column density measurements of N~V and C~IV by factors of 1.2 to 1.9; however, the revised columns have only a minor effect on the parameters derived from our photoionization models. For the first time, we have simultaneous C~IV and N~V columns for component 1 (at -1040 km s-1), and find that this component cannot be an X-ray warm absorber, contrary to our previous claim (based on nonsimultaneous observations of N~V and C~IV). We find that dust-free models of the absorbers severely overpredict the O~VI columns previously obtained with the Far Ultraviolet Spectrograph, and present arguments that this is not likely due to variability. However, models that include dust (and thereby heavily deplete carbon) are successful in matching all of the observed ionic columns, and result in substantially lower ionization parameters and total column densities compared to dust-free models. Interestingly, these models yield the exact amount of dust needed to produce the observed reddening of the inner NLR, assuming a Galactic dust to gas ratio. The models produce little O~VII and O~VIII, indicating that none of the dusty UV absorbers is associated with a classic X-ray warm absorber.

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