Impact of the reduced speed of light approximation on ionization front velocities in cosmological simulations of the epoch of reionization
Impact of the reduced speed of light approximation on ionization front velocities in cosmological simulations of the epoch of reionization
复制标题
再电离时代宇宙学模拟中光速近似降低对电离前沿速度的影响
DOI：
--
复制
发表时间：
2018
影响因子：
6.5
通讯作者：
Joseph S W Lewis
中科院分区：
文献类型：
--
作者：
N. Deparis;D. Aubert;P. Ocvirk;J. Chardin;Joseph S W Lewis
上下文耦合辐射流体动力学模拟的时代的再电离的目的是再现电离前沿的传播在过渡之前的HII区域的重叠。许多这些模拟使用基于矩的方法来跟踪辐射传输过程，使用显式求解器，因此受到严格的稳定性条件，关于光速，这意味着一个很大的计算成本。通过假设光速降低可以降低成本，这种近似现在被广泛用于产生大规模的再电离模拟。
目标。我们测量电离前沿传播的模拟时代的再电离。特别是，我们希望区分锋面进入星系际介质的不同阶段。我们还研究了这些阶段和它们的属性是如何受到光速降低的影响的。
方法.我们介绍了一种新的方法来估计和比较的基础上的再电离红移图的电离锋速度。我们将其应用到一组宇宙学模拟的再电离使用一组降低的光速，并测量在再电离过程中的电离前沿速度的演变。我们只考虑了模型中的再电离是由模拟中创建的源驱动的，没有外部均匀电离背景的潜在贡献。
结果我们发现，电离前沿的进展，通过两个阶段的过程中，第一阶段在低速度的前端出现从高密度区域和第二个稍后的阶段之前的重叠，在此期间，前端速度增加接近光速。例如，使用一组8 Mpc h−3的小型模拟，我们发现0.3c的最小速度能够在此特定背景下模拟这两个阶段，而不会产生重大影响。 低至0.05c的值可以模拟第一低速阶段，但限制了以后的加速度。较低的值始终修改前速度的分布。使用另一组更大的64 Mpc h−3体积的模拟，更好地解释了遥远的来源，我们发现光速的降低对再电离时间和欠密度区域的波前速度有更大的影响，这些区域在后期被再电离，并被遥远的来源产生的辐射扫过。 相反，在具有缓慢锋的密集区域中测量的相同量对c值不太敏感。虽然由降低光速引入的差异可以通过包含额外的UV背景来减少，但我们希望这些结论在模拟由内部源驱动的再电离的情况下是鲁棒的。
Context. Coupled radiative-hydrodynamics simulations of the epoch of reionization aim to reproduce the propagation of ionization fronts during the transition before the overlap of HII regions. Many of these simulations use moment-based methods to track radiative transfer processes using explicit solvers and are therefore subject to strict stability conditions regarding the speed of light, which implies a great computational cost. The cost can be reduced by assuming a reduced speed of light, and this approximation is now widely used to produce large-scale simulations of reionization.
Aims. We measure how ionization fronts propagate in simulations of the epoch of reionization. In particular, we want to distinguish between the different stages of the fronts’ progression into the intergalactic medium. We also investigate how these stages and their properties are impacted by the choice of a reduced speed of light.
Methods. We introduce a new method for estimating and comparing the ionization front speeds based on maps of the reionization redshifts. We applied it to a set of cosmological simulations of the reionization using a set of reduced speeds of light, and measured the evolution of the ionization front speeds during the reionization process. We only considered models where the reionization is driven by the sources created within the simulations, without potential contributions of an external homogeneous ionizing background.
Results. We find that ionization fronts progress via a two-stage process, the first stage at low velocity as the fronts emerge from high density regions and a second later stage just before the overlap, during which front speeds increase close to the speed of light. For example, using a set of small 8 Mpc h−3 simulations, we find that a minimal velocity of 0.3c is able to model these two stages in this specific context without significant impact. Values as low as 0.05c can model the first low velocity stage, but limit the acceleration at later times. Lower values modify the distribution of front speeds at all times. Using another set of simulations with larger 64 Mpc h−3 volumes that better account for distant sources, we find that reduced speed of light has a greater impact on reionization times and front speeds in underdense regions that are reionized at late times and swept by radiation produced by distant sources. Conversely, the same quantities measured in dense regions with slow fronts are less sensitive to c∼ values. While the discrepancies introduced by reduced speed of light could be reduced by the inclusion of an additional UV background, we expect these conclusions to be robust in the case of simulations with reionizations driven by inner sources.
Illustris 宇宙中的氢再电离
影响因子：
4.8
作者：
Bauer A
通讯作者：
Bauer A
DOI：
10.3847/2041-8213/aab14d
发表时间：
2018
期刊：
The Astrophysical Journal Letters
影响因子：
--
作者：
Aubert D
通讯作者：
Aubert D
DOI：
10.3847/1538-4357/ab0d83
发表时间：
2019
期刊：
The Astrophysical Journal
影响因子：
--
作者：
D’Aloisio, Anson;McQuinn, Matthew;Maupin, Oliver;Davies, Frederick B.;Trac, Hy;Fuller, Spencer;Upton Sanderbeck, Phoebe R.
通讯作者：
Upton Sanderbeck, Phoebe R.