Metallicity Evolution of Damped Lyα Systems in ΛCDM Cosmology
Metallicity Evolution of Damped Lyα Systems in ΛCDM Cosmology
复制标题
ΛCDM 宇宙学中阻尼 Lyα 系统的金属丰度演化
DOI：
10.1086/378881
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发表时间：
2002
期刊：
影响因子：
--
通讯作者：
A. Wolfe
中科院分区：
文献类型：
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作者：
R. Cen;J. Ostriker;J. Prochaska;A. Wolfe
利用一个新的、高质量分辨率（Δmb = 105.5 M）的流体动力学模拟方法，对一个空间平坦的ΛCDM宇宙学模型进行了详细的微观物理和星系形成过程的模拟，包括辐射屏蔽、能量沉积、来自超新星的金属富集和相关的金属冷却/加热，计算了阻尼Lyα系统（DLAs）的金属丰度演化，并发现与观测结果相当吻合.特别是，所观察到的DLA金属丰度的缓慢演变自然发生在模拟的物理和观测选择的综合影响的结果。缓慢的金属丰度演变是由于随着时间的增加，最高金属丰度系统稳定地转变为“星系”，从而耗尽了这一类别，而所有较低金属丰度系统单独显示金属丰度增加。虽然DLA金属丰度随红移的变化趋势与观测结果吻合较好，但在探测的红移范围内（z = 0-5），模拟DLA的平均金属丰度似乎比观测值高0.3-0.5 dex。我们的研究表明，这种差异可能归因于观测选择效应，由于尘埃遮蔽。如果我们考虑到尘埃遮蔽效应，我们的模型再现了所观察到的金属丰度演化的幅度和斜率。我们发现，DLAs不是一个简单的人口，但探测一系列不同的系统，并与红移的混合变化。DLA的平均光度LDLA（z），以红移L*（z）的典型星系光度为单位，即z，随着红移从z = 3下降到0，从1.1下降到0.5，但是平均DLA系统的绝对光度在同一时间段内从0.1L*（z = 0）增加到0.5L*（z = 0）。从z = 5到z = 1，气相中大约50%的金属都处于DLAs中，在z ≤ 1到z = 0时，金属会迅速下降到20%左右，因为金属会被卷入星系际介质（IGM）中较热的成分，并被锁定在恒星中。虽然不是本研究的主要重点，我们发现，该模型提供了很好的匹配观测相对于柱密度分布和中性气体含量的演变，如果考虑到相同的尘埃遮蔽。我们发现ΩDLA，comp = 1-3 × 10-3，具体取决于灰尘遮蔽的影响。
Using a new, high mass resolution (Δmb = 105.5 M☉) hydrodynamic simulation of a spatially flat ΛCDM cosmological model with detailed microphysics and galaxy formation, including radiation shielding, energy deposition, and metal enrichment from supernovae and associated metal cooling/heating, we compute the metallicity evolution of damped Lyα systems (DLAs) and find a reasonable agreement with observations. In particular, the observed slow evolution of the DLA metallicity occurs naturally in the simulation as a result of the combined effects of physical and observational selection. The slow metallicity evolution is caused by the steady transformation, with increasing time, of the highest metallicity systems to "galaxies," thus depleting this category, while all the lower metallicity systems show, individually, an increase in metallicity. Although the trend of DLA metallicity with redshift is in good agreement with observations, it appears that the average metallicity of simulated DLAs is higher than observed by 0.3-0.5 dex in the probed redshift range (z = 0-5). Our study indicates that this difference may be attributed to observational selection effects due to dust obscuration. If we allow for a dust obscuration effect, our model reproduces the observed metallicity evolution in both amplitude and slope. We find that DLAs are not a simple population but probe a range of different systems, and the mix changes with redshift. The median luminosity of a DLA, LDLA(z), in units of typical galaxy luminosity at that redshift, L*(z), that is, z, decreases from 1.1 to 0.5 as redshift declines from z = 3 to 0, but the absolute luminosity of the median DLA system increases in the same interval by a factor of 5 from 0.1L*(z = 0) to 0.5L*(z = 0). About 50% of all metals in the gaseous phase is in DLAs at all times from z = 5 to z = 1, making a rapid downturn at z ≤ 1 to ~20% by z = 0, as metals are swept into the hotter components of the intergalactic medium (IGM) as well as locked up in stars. While not the primary focus of this study, we find that the model provides good matches to observations with respect to column density distribution and evolution of neutral gas content, if the same dust obscuration is taken into account. We find ΩDLA,comp = 1-3 × 10-3, depending on the effect of dust obscuration.