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Session 25 - Seyfert Galaxies.
Oral session, Wednesday, January 07

[25.02] An Analysis of the Velocity Dependence of BLR Emission Line Ratios from HST and Optical Spectra

S. A. Snedden, C. M. Gaskell (U. Nebraska)

We present the results of a study of quasar emission line ratios as a function of projected velocity. Eight AGN with high S/N optical and UV spectra were analyzed with the intent of deducing the physical characteristics of the regions associated with high and low ionization emission lines as a function of velocity. The C III]/C IV/Ly\alpha ratios show almost no velocity dependence. We compare the observed line ratios to predictions from photoionization models for the C III]/C IV and Ly\alpha/C IV ratios. From these we establish values for the hydrogen density, n_H, and the ionization parameter, U, in the C^++/C^+++ zones of the BLR cloud. We obtain typical values of n_H \simeq 3 \times 10^10 cm^-3 and U \simeq 0.3 for solar abundance clouds. Our deduced n_H increases by almost an order of magnitude if we assume 5 Z_\sun abundances. The deduced ionization parameter shows a slight decrease with increasing abundances. n_H and U show almost no velocity dependence. The conditions inferred from the C III]/C IV/Ly\alpha ratios fail to reproduce the observed Balmer/Lyman profile ratios.

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