Abundances in the Associated System of HS 1946+7658

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Session 45 -- Metallicity in AGN and the Near-AGN Environment
Oral presentation, Wednesday, June 14, 1995, 2:00pm - 5:30pm

[45.05] Abundances in the Associated System of HS 1946+7658

Todd M. Tripp (U.Wisconsin-Madison), Limin Lu (Caltech), Blair D. Savage (U.Wisconsin-Madison)

We have obtained high signal-to-noise echelle spectra of the radio-quiet QSO HS 1946+7658 ($z_{{\rm em}}$ = 3.051) with the KPNO 4m telescope. We detect 11 metal systems in the direction of this QSO including associated systems at $z_{{\rm abs}}$ = 3.03841 and $z_{{\rm abs}}$ = 3.0496,3.0504. The prominent associated system at $z_{{\rm abs}}$ = 3.0496,3.0504 is detected in H I, C II, C IV, Si II, Si III, Si IV, Al II, Al III, and N V, and all of these species show two components; both C IV lines show four components. The high ion column density ratios in this associated system differ dramatically from the high ion ratios observed in the Galactic halo. For example, $N$(C IV)/$N$(Si IV) $>$ 50 in one component. This is not surprising given the extraordinary luminosity of the QSO. To study the ionization and abundances in this associated system, we compare the observed column densities to a series of CLOUDY models in which photoionization by the QSO is the dominant ionization mechanism. For the input radiation field, we have used the various spectral energy distributions of HS 1946+7658 observed by Kuhn et al. (1995, ApJ, 438, 643). The model that best fits the observed column densities of singly and doubly ionized species has solar relative and absolute abundances, but models with absolute metallicities a few times greater than solar fit comparably well. None of the models produce enough Si IV and C IV, but the QSO flux near the ionization potentials of these ions is uncertain. The high metallicity implied by the best models suggests that the associated absorption occurs near the nucleus of the QSO where the star formation rate is likely to be enhanced, but the ionization parameter from the best model combined with a density upper limit from C II* implies that the distance between the QSO and the associated system is greater than 300 kpc. Also, the C IV profile has the kinematic signature of a rotating object intercepted edge-on, which seems more likely to occur in a galaxy exterior to the quasar. We briefly discuss possible explanations of these discordant conclusions.

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