The Transmission Correlation in the QSO LY alpha Forest Produced by Finite Width Lines
Abstract
The transmission of a quasar spectrum (flux divided by the continuum) is correlated because of the finite width of absorption lines. We describe a technique for calculating the transmission correlation function produced by randomly distributed lines. We also introduce straightforward procedure for measuring the pixelpixel transmission correlation function ξ_pp_ directly from observed quasar spectra. We apply the method to 12 Sargent, Boksenberg, & Steidel QSO spectra and compare these with theoretical transmission correlation functions and with ξ_pp_ measured from computersimulated quasar spectra of Lyα forest models with Poissondistributed lines. The simulations are designed to mimic the observed spectrum as closely as possible, with the same wavelength sampling, instrumental resolution, continuum and noise properties. The comparisons with line distributions that are power laws in column density and redshift, and Gaussians in line width b reveal an excess in the observed ξ_pp_ at {DELTA}ν~ 150 km s^1^, if we adopt the Carswell et al. (1991) parameters for the Gaussian (mean b_0_ = 30 km s^1^, dispersion σ_b_ = 10 km s^1^). One possibility is that the Lyα forest lines are actually clustered at velocity separation scales {DELTA}ν~150 km s^1^. Another possibility we explore here is that the bdistribution has more large b clouds and a larger dispersion. We find the observed ξ_pp_ is barely consistent with b_0_ = 40 km s^1^ and σ_b_ = 25 km s^1^ We show that the measured ξ_pp_ is relatively insensitive to the noise level and to errors in the continuum determination, unlike the traditional line counting methods, where the outcome is quite vulnerable to both. It also requires no line deblending and thus offers a powerful tool for extracting information from the crowded Lyα forest.
 Publication:

The Astrophysical Journal
 Pub Date:
 March 1994
 DOI:
 10.1086/173791
 Bibcode:
 1994ApJ...423...73Z
 Keywords:

 Absorption Spectra;
 Computerized Simulation;
 Cosmology;
 Line Spectra;
 Lyman Alpha Radiation;
 Quasars;
 Intergalactic Media;
 Pixels;
 Red Shift;
 Spectrum Analysis;
 Astrophysics;
 COSMOLOGY: THEORY;
 GALAXIES: INTERGALACTIC MEDIUM;
 GALAXIES: QUASARS: ABSORPTION LINES