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D. Casebeer, K. Leighly (University of Oklahoma)
The primary determinant of the optical and UV emission line ratios from Active Galactic Nuclei (AGN) is the dimensionless ionization parameter, defined as the ratio of the photon density to the gas density (or pressure). However, secondary effects including the shape of the ionizing continuum should also play a role. This is potentially important since the line ratios may provide a way to infer the shape of the continuum in the unobservable EUV wavelength range. With this premise, we developed a project designed to test systematically the influence of the spectral energy distribution (SED) on emission line equivalent widths and ratios.
This project uses the spectral synthesis code Cloudy for a one-zone model and a simple SED parameterized by the big blue bump cutoff temperature kT. Also \alphaox, the slope between 2500 Å/\ and 2~keV was constrained. Models were run for a range of cutoff temperatures from 10\rm\,eV to 350\rm\,eV, a fixed hydrogen density log(Hden)=10, and for a range of ionization parameters. Two different hydrogen column densities were used: the thinner one was truncated at the He+2 to He+ ionization boundary, and the thicker one continued past the hydrogen ionization front to the C+ to C boundary. The results indicate that the high-ionization lines show a cutoff temperature dependence for all values of the ionization parameter. Metallicity and density indicators are found to be somewhat dependent on cutoff temperature. We apply the results to RE~1034+39, a narrow-line Seyfert 1 galaxy with an unusually hot blue bump.
This work is supported by NASA grants NAG5-10048 (FUSE) and NAG5-10171 (LTSA).
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.