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Title:
Remeasurement of the H I Gunn-Peterson Effect toward QSO PKS 1937-101 with Keck Observations
Authors:
Fang, Yihu; Fan, Xiaoming; Tytler, David; Crotts, Arlin P. S.
Affiliation:
AA(Department of Astronomy, Columbia University, 538 West 120th Street, New York, NY 10027.), AB(Department of Physics, and Center for Astrophysics and Space Sciences, University of California at San Diego, La Jolla, CA 92093.), AC(Department of Physics, and Center for Astrophysics and Space Sciences, University of California at San Diego, La Jolla, CA 92093.), AD(Department of Astronomy, Columbia University, 538 West 120th Street, New York, NY 10027.)
Publication:
The Astrophysical Journal, Volume 497, Issue 1, pp. 67-71. (ApJ Homepage)
Publication Date:
04/1998
Origin:
APJ; UCP
Astronomy Keywords:
COSMOLOGY: OBSERVATIONS, GALAXIES: INTERGALACTIC MEDIUM, GALAXIES: QUASARS: ABSORPTION LINES, GALAXIES: QUASARS: INDIVIDUAL ALPHANUMERIC: PKS 1937-, 01, Cosmology: Observations, Galaxies: Intergalactic Medium, Galaxies: Quasars: Absorption Lines, Galaxies: Quasars: Individual: Alphanumeric: PKS 1937-101
Abstract Copyright:
(c) 1998: The American Astronomical Society
DOI:
10.1086/305431
Bibliographic Code:
1998ApJ...497...67F

Abstract

We present the first measurement of the H I Gunn-Peterson effect using the Keck 10 m telescope, observing the high-redshift QSO PKS 1937-101 (z = 3.787). The high-resolution echelle (HIRES) spectra, with FWHM ~15 km s-1 and a signal-to-noise ratio (S/N) ~50 per spectral resolution element, allows us to resolve many weak lines down to NH I = 1012 cm-2, thus reducing the line-blanketing problem compared with previous data. Based on intensity-distribution analysis, we find that a maximum likelihood best fit yields a Gunn-Peterson type of opacity τGP = 0.113 +/- 0.020 in addition to a power-law Lyα absorption-line population with β of 1.7 down to NH I = 1012 cm-2. There remains systematic uncertainty in this result because of problems extrapolating the spectral continuum from the red side of the Lyα emission line. This is consistent with the previous study of the same QSO in low S/N data using weighted intensity function analysis (Fang & Crotts 1995). It indicates that this previous method succeeds in measuring the Lyα forest continuum level at low S/N, which is essential in extending the technique to possible fainter QSOs with minimum emission-line contamination for reliable continuum extrapolation. We further discuss problems of severe line blanketing, even in Keck spectra for QSOs at z >= 4.5, and show the effectiveness of the weighted intensity function method in measuring continuum levels in extremely crowded Lyα absorption spectra for redshifts as high as z > 5.
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