Remeasurement of the H i Gunn-Peterson Effect toward QSO PKS 1937-101 with Keck Observations

Details Remeasurement of the H i Gunn-Peterson Effect toward QSO PKS 1937-101 with Keck Observations Remeasurement of the H i Gunn-Peterson Effect toward QSO PKS 1937-101 with Keck Observations

Apr 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998apj...497...67f&link_type=abstract

Astrophysical Journal v.497, p.67

Astronomy and Astrophysics

Astronomy

6

Cosmology: Observations, Galaxies: Intergalactic Medium, Galaxies: Quasars: Absorption Lines, Galaxies: Quasars: Individual Alphanumeric: Pks 1937-, 01

Scientific paper

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 tau GP = 0.113 +/- 0.020 in addition to a power-law Ly alpha absorption-line population with beta 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 Ly alpha 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 Ly alpha 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 Ly alpha absorption spectra for redshifts as high as z > 5.

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