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Broad NE 8 lambda 774 emission from quasars in the HST-FOS snapshot survey (ABSNAP)We discuss the strength and frequency of broad Ne VIII lambda 774 emission from quasars measured in the Hubble Space Telescope Faint Object Spectrograph (HST-FOS) snapshot survey (Absnap). Five sources in the survey have suitable redshifts (0.86 less than or equal to Z(sub em) less than or equal to 1.31), signal-to-noise ratios and no Lyman limit absorptions. Three of the five sources have a strong broad emission line near 774 A (rest), and the remaining two sources have a less securely measured line near this wavelength. We identify these lines with Ne VIII lambda 774 based on the measured wavelengths and theoretical estimates of various line fluxes (Hamann et al. 1995a). 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 in quasars, with typical strengths between approximately 25% and approximately 200% of O VI lambda 1034. These Ne VIII lambda 774 measurements imply that the broad emission line regions have a much hotter and more highly ionized component than previously recognized. They also suggest that quasar continua have substantial ionizing flux out to energies greater than 207 eV (greater than 15.2 ryd, lambda less than 60 A). Photoionization calculations using standard incident spectra indicate that the Ne VIII emission requires ionization parameters U greater than or = 5, total column densities N(sub H) greater than or = 10(sub 22)/sq cm and covering factors greater than or = 25%. The temperatures could be as high as approximately 10(exp 5) K. If the gas is instead collisionally ionized, strong Ne VIII would imply equilibrium temperatures in the range approximately 400,000 less than or approximately = T(sub e) less than or approximately = 10(exp 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.
Document ID
19950054414
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Hamann, Fred
(University of California, San Diego, La Jolla, CA United States)
Zuo, Lin
(University of California, San Diego, La Jolla, CA United States)
Tytler, David
(University of California, San Diego, La Jolla, CA United States)
Date Acquired
August 16, 2013
Publication Date
May 10, 1995
Publication Information
Publication: Astrophysical Journal, Part 2 - Letters
Volume: 444
Issue: 2
ISSN: 0004-637X
Subject Category
Astronomy
Accession Number
95A86013
Funding Number(s)
CONTRACT_GRANT: NAS5-26555
CONTRACT_GRANT: NAGW-2119
CONTRACT_GRANT: NAG5-1630
Distribution Limits
Public
Copyright
Other

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