Shattering of Cosmic Sheets due to Thermal Instabilities: A Formation Channel for Metal-free Lyman Limit Systems
Shattering of Cosmic Sheets due to Thermal Instabilities: A Formation Channel for Metal-free Lyman Limit Systems
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热不稳定性导致的宇宙片破碎：无金属莱曼极限系统的形成通道
DOI：
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发表时间：
2019
影响因子：
4.9
通讯作者：
F. van de Voort
中科院分区：
文献类型：
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作者：
Nir Mandelker;F. C. van den Bosch;V. Springel;F. van de Voort
我们提出了一个新的宇宙学放大模拟，其中放大区域由两个维里质量为Mv <$5 × 1012 M <$的晕和一个大约兆秒差距长的宇宙细丝组成。利用这个模拟，我们研究了星系际介质的演化，在这两个晕之间的前所未有的分辨率。在5 μ z的位置。这一层在z = 5处坍缩，是由两个较小的层合并而成的。这次合并产生的强烈激波导致了激波后区域的热不稳定性，并导致了片层的破碎，产生了千帕尺度的云，温度为T <$2 × 104 K，密度为n <$10 −3 cm−3，这些云的压力被限制在T <$106 K，n <$10 −5 cm−3的热介质中。当从正面观察时，这些冷云的中性氢柱密度NH i > 1017.2 cm−2，使它们可以作为莱曼极限系统被探测到，尽管它们位于任何晕的维里半径之外，甚至在致密的细丝之外。它们的化学成分是原始的，金属含量为零，与最近观察到的几个系统相似。由于这些系统远离任何星系形成，这些结果是强大的星系形成物理学，纯粹从大尺度结构和辐射冷却的崩溃，提供足够的空间分辨率是可用的。
We present a new cosmological zoom-in simulation, where the zoom region consists of two halos with virial mass Mv ∼ 5 × 1012M⊙ and an approximately megaparsec long cosmic filament connecting them at z ∼ 2. Using this simulation, we study the evolution of the intergalactic medium in between these two halos at unprecedented resolution. At 5 ≳ z ≳ 3, the two halos are found to lie in a large intergalactic sheet, or “pancake,” consisting of multiple coplanar dense filaments along which nearly all halos with Mv > 109M⊙ are located. This sheet collapses at z ∼ 5 from the merger of two smaller sheets. The strong shock generated by this merger leads to thermal instabilities in the postshock region, and to a shattering of the sheet resulting in ≲ kiloparsec-scale clouds with temperatures of T ≳ 2 × 104 K and densities of n ≳ 10−3 cm−3, which are pressure confined in a hot medium with T ∼ 106 K and n ≳ 10−5 cm−3. When the sheet is viewed face-on, these cold clouds have neutral hydrogen column densities of NH i > 1017.2 cm−2, making them detectable as Lyman limit systems, though they lie well outside the virial radius of any halo and even well outside the dense filaments. Their chemical composition is pristine, having zero metallicity, similar to several recently observed systems. Since these systems form far from any galaxies, these results are robust to galaxy formation physics, resulting purely from the collapse of large-scale structure and radiative cooling, provided sufficient spatial resolution is available.