论文标题
将宇宙学吸收连接到强大的Lyman-Alpha吸收器
Connecting cosmological accretion to strong Lyman-alpha absorbers
论文作者
论文摘要
我们基于适用于球形系统的相似解决方案，提出了一种将气体宇宙学积聚到暗物质光环上的分析模型。执行简化的辐射传输，我们计算积聚气体如何从电离背景进行自shield时越来越中性，并获得$ n _ {\ rm hi} $作为影响参数的函数。所得的列密度分布函数（CDDF）与观测值非常吻合。分析表达阐明了（1）为什么在质量大范围内的晕孔在巨大范围内同样贡献了CDDF，以及（2）为什么CDDF在RedShift范围内少于$ z = 2 \ rightarrow 5 $的红移而演变很少。我们表明该模型还可以预测合理的DLA线宽度（$ v_ {90} $），偏置和分子分数。在CDDF上集成会产生中性气的质量密度，$ω_ {\ rm hi} $，这与观测很吻合。 $ω_ {\ rm hi}（z）$即使对光环的积聚率不断发展，也是恒定的。我们表明，这是因为流入气体中性的时间的比例取决于光环的动力学时间，光晕时间与增生率成反比。简单模型封装了宇宙学模拟的结果，表明大多数Lyman-Limit系统和阻尼的Lyman-Alpha吸收器与气体的宇宙学积聚有关。
We present an analytical model for the cosmological accretion of gas onto dark matter halos, based on a similarity solution applicable to spherical systems. Performing simplified radiative transfer, we compute how the accreting gas turns increasingly neutral as it self-shields from the ionising background, and obtain the column density, $N_{\rm HI}$, as a function of impact parameter. The resulting column-density distribution function (CDDF) is in excellent agreement with observations. The analytical expression elucidates (1) why halos over a large range in mass contribute about equally to the CDDF as well as (2) why the CDDF evolves so little with redshift in the range $z=2\rightarrow 5$. We show that the model also predicts reasonable DLA line-widths ($v_{90}$), bias and molecular fractions. Integrating over the CDDF yields the mass density in neutral gas, $Ω_{\rm HI}$, which agrees well with observations. $Ω_{\rm HI}(z)$ is nearly constant even though the accretion rate onto halos evolves. We show that this occurs because the fraction of time that the inflowing gas is neutral depends on the dynamical time of the halo, which is inversely proportional to the accretion rate. Encapsulating results from cosmological simulations, the simple model shows that most Lyman-limit system and damped Lyman-alpha absorbers are associated with the cosmological accretion of gas onto halos.
