Voigt‐Profile Analysis of the Lyα Forest in a Cold Dark Matter Universe

Abstract

We use an automated Voigt-profile fitting procedure to extract statistical properties of the Ly alpha forest in a numerical simulation of an Omega = 1, cold dark matter (CDM) universe. Our analysis method is similar to that used in most observational studies of the forest, and we compare the simulations to recently published results derived from Keck HIRES spectra. With the Voigt-profile decomposition analysis, the simulation reproduces the large number of weak lines (NH I < 20 km s-1) than are seen in the data. The first result is sensitive to our adopted normalization of the mean Ly alpha optical depth, and the second is sensitive to our assumption that helium reionization has not significantly raised gas temperatures at z = 3. It is therefore too early to say whether these discrepancies indicate a fundamental problem with the high-redshift structure of the Omega = 1 CDM model or reflect errors of detail in our modeling of the gas distribution or the observational procedures.