CDROM/APJ/V457/P102 Ly-Alpha Forest Spectra Sim. Analysis. I. (Dobrzycki+ 1996) ================================================================================ Simulation Analysis of Ly-Alpha Forest Spectra. I. Empirical Description at z ~ 3 Adam Dobrzycki and Jill Bechtold <1996, ApJ, 457, 102> =1996ApJ...457..102D ================================================================================ Abstract: We present moderate-resolution (~50 km/s 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 d"N"/dN proportional to N^(-beta) and d"N"/db proportional to exp[-(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 = 30 +/- 15 km/s. 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 , 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. Keywords: cosmology: observations -- intergalactic medium -- quasars: absorption lines File Summary: -------------------------------------------------------------------------------- File Name Lrecl Records Explanations -------------------------------------------------------------------------------- q1206119.dat 71 153 Line list for Q1206+119 q1225017.dat 71 109 Line list for Q1225-017 q1315472.dat 71 107 Line list for Q1315+472 q1607183.dat 71 118 Line list for Q1607+183 q1623268.dat 71 111 Line list for Q1623+268 q1700643.dat 71 133 Line list for Q1700+643 q1946770.dat 71 119 Line list for Q1946+770 table2.tex 94 936 AASTeX version of line lists for all quasars -------------------------------------------------------------------------------- Byte-by-byte Description of file: q1206119.dat q1225017.dat q1315472.dat q1607183.dat q1623268.dat q1700643.dat q1946770.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 3 I3 --- Num *[]? Line number 4-12 F9.2 0.1nm Lambda []? Wavelength 13-20 F8.3 0.1nm W []? Equivalent width 21-27 F7.3 0.1nm e_W []? Equivalent width error 28-29 2X --- --- Blank 30-49 A20 --- Ident *Identification 50-51 2X --- --- Blank 52-71 A20 --- Poss *Possible identification -------------------------------------------------------------------------------- Notes for file: table2.dat -------------------------------------------------------------------------------- Num: Line number. If this field is blank, then the data in fields Ident and Poss are continuations of the previous record. Ident, Poss: Line indentification and possible identification. The format of the identifications includes the ion, wavelength, and redshift, e.g. "Si IV 1402 z=2.5725". -------------------------------------------------------------------------------- ================================================================================ (End) Lee Brotzman [ADS] 22-Apr-96