标题： 冷暗物质宇宙中Lyman-alpha森林的Voigt谱线分析 显示英文标题

标题： Voigt-Profile Analysis of the Lyman-alpha Forest in a Cold Dark Matter Universe

摘要： 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 ($N_{\rm HI}\la 10^{13}\cdunits$) found in the HIRES spectra. The column density distribution evolves significantly between $z=3$ and $z=2$, with the number of lines at fixed column density dropping by a factor $\sim 1.6$ in the range where line blending is not severe. 在$z=3$时，$b$参数分布的中位数为$35 \kms$，分散程度为$20 \kms$，与观测值基本一致。 我们新分析结果与近期数据的对比加强了早期的论断，即\lya 森林在等级结构形成过程中自然出现，是被光电离的气体落入暗物质势阱的结果。 然而，模拟森林与HIRES结果之间存在两个统计上显著的差异：模型在$z=3$处产生的线条数量过多，超出观测值$\sim 1.5-2$倍，而且它产生的窄线（$b<20 \kms$）比数据中观察到的更多。 第一个结果对平均\lya 光学深度归一化的选择敏感，而第二个结果则受到我们假设氦再电离并未显著提高$z=3$处气体温度的影响。 因此，现在就断言这些差异是否表明高红移下$\Omega=1$冷暗物质模型的基本结构存在问题，或者反映我们对气体分布建模或观测程序细节上的错误，还为时过早。 显示英文摘要

摘要： 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 ($N_{\rm HI}\la 10^{13}\cdunits$) found in the HIRES spectra. The column density distribution evolves significantly between $z=3$ and $z=2$, with the number of lines at fixed column density dropping by a factor $\sim 1.6$ in the range where line blending is not severe. 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 \lya forest arises naturally in hierarchical structure formation as photoionized gas falls into dark matter potential wells. However, there are two statistically signficant discrepancies between the simulated forest and the HIRES results: the model produces too many lines at $z=3$ by a factor $\sim 1.5-2$, and it produces more narrow lines ($b<20 \kms$) than are seen in the data. The first result is sensitive to our adopted normalization of the mean \lya 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 procedure.