BROAD NE-VIII LAMBDA-774 EMISSION FROM QUASARS IN THE HST-FOS SNAPSHOT SURVEY (ABSNAP)

We discuss the strength and frequency of broad Ne VIII lambda 774 emis sion from quasars measured in the HST-FOS snapshot survey (Absnap). Fi ve sources in the survey have suitable redshifts (0.86 less than or eq ual to z(em) less than or equal to 1.31), signal-to-noise ratios and n o Lyman limit absorptions. Three of the five sources have a strong bro ad emission line near 774 Angstrom (rest), and the remaining two sourc es have a less securely measured line near this wavelength. We identif y these lines with Ne VIII lambda 774 based on the measured wavelength s and theoretical estimates of various line fluxes (Hamann et al. 1995 a). Secure Ne VIII detections occur in both radio-loud and radio-quiet sources. We tentatively conclude that broad Ne VIII lambda 774 emissi on is common in quasars, with typical strengths between similar to 25% and similar to 200% of O VI lambda 1034. These Ne VII lambda 774 meas urements imply that the broad emission line regions have a much hotter and more highly ionized component than previously recognized. They al so suggest that quasar continua have substantial ionizing flux out to energies greater than 207 eV (>15.2 ryd, lambda < 60 Angstrom). Photoi onization calculations using standard incident spectra indicate that t he Ne vm emission requires ionization parameters U greater than or sim ilar to 5, total column densities N-H greater than or similar to 10(22 ) cm(-2) and covering factors greater than or similar to 25%. The temp eratures could be as high as similar to 10(5) K. If the gas is instead collisionally ionized, strong Ne vm would imply equilibrium temperatu res in the range similar to 400,000 less than or similar to T-e less t han or similar to 10(6) K. In either case, the highly ionized Ne VIII emission regions would appear as X-ray ''warm absorbers'' if they lie along our line of sight to the X-ray continuum source.