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For refcode 1996ApJ...457..102D:
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1996ApJ...457..102D SIMULATION ANALYSIS OF Ly{alpha} FOREST SPECTRA. I. EMPIRICAL DESCRIPTION AT z ~ 3 ADAM DOBRZYCKI Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138; adobrrycki@cfa.harvard.edu AND JILL BECHTOLD Steward Observatory, University of Arizona, Tucson, AZ 85721 ;jbechtold@as.arizona.edu Received 1995 February 6; accepted 1995 July 28 ABSTRACT We present moderate-resolution (~50 km s^-1^ FWHM) spectra of the Ly{alpha} forest for seven quasars with redshifts ranging from 2.53 to 3.13, obtained with the Blue Spectrograph and photon-counting Reticon at the Multiple Mirror Telescope. Combined with spectra of 10 other quasars presented elsewhere, we have characterized the distribution of cloud properties in a way which was designed to minimize any subjective part of the analysis. We used artificial absorption spectra, with the same resolution, sampling and signal-to-noise ratio as a function of wavelength as the actual data. Distributions of the physical parameters of the Ly{alpha} clouds, namely, the neutral hydrogen column density (N) and Doppler parameter (b), were approximated with dN/dN is proportional to N^-{beta}^ and dN/db is proportional to exp [-(b - <b>)^2^/2 {sigma}_b_^2^], respectively. We constructed a grid of simulated spectra with different input parameters. Comparison of properties of the simulated spectra with the observed spectra yielded acceptable ranges of parameters. Our technique differs from previous similar work in that we use the information contained in the distribution of the strength of the absorption in each resolution element and the distribution of separations between absorption complexes. We derive {beta} = 1.4 +/- 0.1 for N ranging from 10^13^ to 10^16^ cm^-2^ and <b> = 30 +/- 15 km s^-1^, Most previous studies based on line lists indicated {beta} = 1.7-1.9. We attribute this difference to flattening of the column density distribution for low N, recently confirmed by higher resolution observations. Our result for <b>, though consistent with values quoted in the literature, is of lower significance, since it is less than the resolution of our spectra. We conclude by commenting on the importance of line blending in data sets of this kind. Subject headings: cosmology: observations - intergalactic medium - quasars: absorption lines
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