Recovering the topology of the intergalactic medium at z ~ 2
Recovering the topology of the intergalactic medium at z ~ 2
复制标题
恢复 z ~ 2 处星际介质的拓扑
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
T. Sousbie
中科院分区：
文献类型：
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作者：
S. Caucci;S. Colombi;C. Pichon;E. Rollinde;P. Petitjean;T. Sousbie
我们研究了如何使用沿着类星体视线观察到的莱曼 α 吸收来重建星际介质 (IGM) 中中性氢的三维密度场，这些类星体在天空投影中相隔 arcmin 距离。我们使用宇宙流体动力学模拟来比较不同领域的拓扑：暗物质、气体和中性氢光学深度，并研究如何从 Pichon 等人实施的维纳插值方法中恢复 IGM 的拓扑。通过功率谱、概率分布函数（PDF）、欧拉特征、相关临界点计数和欠密区域的填充因子，定量分析恢复场的全局统计和拓扑特性。通过定义骨架间距离的概念，使用局部骨架来分析场的局部几何特性。
由于所考虑的尺度上密度分布的近对数正态性质，断层扫描最好根据密度的对数而不是密度本身进行。在大于∼1.4<dLOS>的尺度上，其中<dLOS>是视线之间的平均间隔，重建准确地恢复了气体大尺度密度分布的拓扑特征，特别是丝状结构：重建与精确解之间的骨架间距离小于<dLOS>。在大于反演过程的固有平滑长度的尺度上，恢复的 H i 密度场的功率谱与原始密度场的功率谱很好地匹配，并且 PDF 的低阶矩以及欧拉特征的形状得到了很好的恢复。 PDF 上的积分误差和临界点计数确实很小，对于小于 ∼2.5 弧分的平均视线间隔，积分误差小于 20%。重建与精确解之间的小偏差主要反映了与对数正态行为的偏离，这些行为归因于过密区域中的高度非线性对象。
We investigate how well the three-dimensional density field of neutral hydrogen in the intergalactic medium (IGM) can be reconstructed using the Lyman α absorptions observed along lines-of-sight to quasars separated by arcmin distances in projection on the sky. We use cosmological hydrodynamical simulations to compare the topologies of different fields: dark matter, gas and neutral hydrogen optical depth and to investigate how well the topology of the IGM can be recovered from the Wiener interpolation method implemented by Pichon et al. The global statistical and topological properties of the recovered field are analysed quantitatively through the power spectrum, the probability distribution function (PDF), the Euler characteristics, its associated critical point counts and the filling factor of underdense regions. The local geometrical properties of the field are analysed using the local skeleton by defining the concept of interskeleton distance.
As a consequence of the nearly lognormal nature of the density distribution at the scales under consideration, the tomography is best carried out on the logarithm of the density rather than the density itself. At scales larger than ∼1.4 〈dLOS〉, where 〈dLOS〉 is the mean separation between lines-of-sight, the reconstruction accurately recovers the topological features of the large-scale density distribution of the gas, in particular the filamentary structures: the interskeleton distance between the reconstruction and the exact solution is smaller than 〈dLOS〉. At scales larger than the intrinsic smoothing length of the inversion procedure, the power spectrum of the recovered H i density field matches well that of the original one and the low-order moments of the PDF are well recovered as well as the shape of the Euler characteristic. The integral errors on the PDF and the critical point counts are indeed small, less than 20 per cent for a mean line-of-sight separation smaller than ∼2.5 arcmin. The small deviations between the reconstruction and the exact solution mainly reflect departures from the lognormal behaviour that are ascribed to highly non-linear objects in overdense regions.