Analysis of the Lyman-alpha Forest in Cosmological Simulations Using Voigt-Profile Decomposition

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 ($N_{\rm HI}\la 10^{14} cm^{-2}$) found in the HIRES spectra. At $z=3$, the $b$-parameter distribution has a median of $35\kms$ and a dispersion of $20\kms$, in reasonable agreement with the observed values. The comparison between our new analysis and recent data strengthens earlier claims that the Ly$alpha$ forest arises naturally in hierarchical structure formation as photoionized gas falls into dark matter potential wells.