Strong Ne VIII $\lambda$774 Emission From Quasars in the HST-FOS Snapshot Survey (Absnap)

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Session 27 -- Spectroscopy of AGN I: Narrowlines
Oral presentation, Monday, 9, 1995, 10:00am - 11:30am

[27.04] Strong Ne VIII $\lambda$774 Emission From Quasars in the HST-FOS Snapshot Survey (Absnap)

Fred Hamann, Lin Zuo and David Tytler (UCSD)

We discuss the strength and frequency of broad Ne~VIII $\lambda$774 emission from quasars. Five quasars in the HST-FOS snapshot survey (Absnap) have suitable redshifts (0.86 $\leq$ $z_{em}$ $\leq$ 1.31), signal-to-noise ratios and no Lyman limit absorptions. Three of the five clearly have a strong broad emission line near 774 \AA\ (rest), and the remaining two have less securely measured features near this wavelength. We identify these lines with Ne~VIII based on the measured wavelengths and theoretical estimates of the various line fluxes. Secure Ne~VIII detections occur in both radio-loud and radio-quiet sources. We tentatively conclude that broad Ne~VIII $\lambda$774 emission is common, with typical strengths between $\sim$25\% and $\sim$200\% of O~VI $\lambda$1034.

These Ne~VIII $\lambda$774 detections imply that quasar continuum spectra have substantial flux out to energies $>$207 eV ($>$15.2 Ryd, $\lambda$ $<$ 60 \AA ), and that the broad emission line regions have components that are much hotter and more highly ionized than previously recognized. Photoionization calculations indicate that the ionization parameters are $U$ $\gap$ 10 photons per $e^-$, the total column densities are $N_H$ $\gap$ 10$^{22}$ cm$^{-2}$, and the covering factors are $\gap$25\% for the Ne~VIII emitting gas. The temperatures could exceed 10$^5$ K. These highly ionized emission regions would appear as X-ray ``warm absorbers'' if they lie along our line of sight to the X-ray continuum source. \bigskip

This work was supported by NASA grants NAG 5-1630 and NAGW-2119, and by AR-5292.02-93A and GO-4396.01-92A from the Space Telescope Science Institute.

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