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Session 63 - The Frontiers of Far Ultraviolet Astrophysics - II.
Topical, Oral session, Wednesday, June 10
Sierra/Padre,
The nearest, brightest active galaxies have inspired our current vision of the AGN paradigm. These same galaxies are the ones imaged with HST, have the highest S/N HST and IUE far-UV spectra, and have the best X-ray spectra. Observations at rest-frame wavelengths of 900 to 1200 Å\ permit us to (i) study the continuum shape in the Lyman limit region; (ii) search for intrinsic absorption from neutral hydrogen, molecular hydrogen, and ionized species such as \sc O vi \lambda\lambda1032,1037, \sc C iii \lambda977, and \sc N iii \lambda991; and (iii) measure the strengths of emission lines from these same transitions. Often these spectral features correlate with other properties of these active galaxies such as the morphology of the narrow-line region (NLR) as observed with HST, and X-ray spectral features such as absorption from highly ionized oxygen (\sc O vii and \sc O viii) and soft X-ray excesses. This provides valuable clues to the structure of gas in the near-nuclear regions of AGN. These same spectral features are not visible with HST unless one reaches out to redshifts of 0.15--0.30, or higher. At such high z, the spatial scale is poor (worse than ground-based observations of low-z AGN) and objects are faint (making it difficult to obtain high quality UV and X-ray spectra). The mean luminosity of known AGN at these redshifts is substantially higher, and there are no samples of lower luminosity classes such as Seyfert 2s and LINERs at these redshifts.
I will discuss our current knowledge of the far-UV spectra of the nearest and brightest AGN based on observations obtained with the Hopkins Ultraviolet Telescope and the Hubble Space Telescope, and look forward to what we can learn from observations of the 100 or more AGN that will be visible to the Far Ultraviolet Spectroscopic Explorer (FUSE), currently scheduled for launch early in 1999.
