用于无碰撞N体模拟的新型自适应柔化：消除伪晕
Novel Adaptive softening for collisionless N-body simulations: Eliminating spurious halos
摘要：
我们描述了用于无碰撞$N$ -体模拟的新型自适应软化（NovA）形式，该形式在Ramses自适应网格细化代码中实现。我们引入了一个细化标准，每个细胞内的颗粒分布是足够的各向同性，其转动惯量张量测量。以这种方式，仅当塌陷沿所有三个轴发生时才被细化，从而确保软化$ε$总是单元中最大颗粒间间距的两倍。这种更保守力软化准则的设计是为了最大限度地减少虚假的两体效应，同时保持高的力的分辨率在崩溃的地区的流动。我们测试NovA使用反对称扰动平面波崩溃（“瓦灵尼亚”测试），然后将其应用到温暖的暗物质（WDM）模拟。对于Valinia测试，我们表明，-不像标准的$N$体方法- NovA产生没有数值破碎，同时仍然能够正确地捕捉细焦散和壳周围的塌陷区域。对于WDM模拟，我们发现，诺瓦收敛速度显着比标准的$N$体，产生很少或没有杂散晕小规模。然而，我们表明，确定是否存在晕低于自由流动的质量$M_{\rm fs}$是复杂的事实，我们的晕发现者（AHF）可能不正确地标记一些焦散和纵横交错的细丝晕，而一个或两个特别大规模的细丝出现在任何版本的NovA的细化是允许的片段。这种巨大的细丝可能是物理上不稳定的崩溃，就像无限的、静态的、自引力的圆柱体一样。我们将在即将发表的论文中使用NovA来研究$M_{\rm fs}$以下的晕形成问题;灯丝稳定性;并获得对暗物质温度的新约束。
英文摘要：
We describe a NOVel form of Adaptive softening (NovA) for collisionless $N$-body simulations, implemented in the Ramses adaptive mesh refinement code. We introduce a refinement criterion that the particle distribution within each cell be sufficiently isotropic, as measured by its moment of inertia tensor. In this way, collapse is only refined if it occurs along all three axes, ensuring that the softening $ε$ is always of order twice the largest inter-particle spacing in a cell. This more conservative force softening criterion is designed to minimise spurious two-body effects, while maintaining high force resolution in collapsed regions of the flow. We test NovA using an antisymmetric perturbed plane wave collapse (`Valinia' test) before applying it to warm dark matter (WDM) simulations. For the Valinia test, we show that -- unlike the standard $N$-body method -- NovA produces no numerical fragmentation while still being able to correctly capture fine caustics and shells around the collapsing regions. For the WDM simulations, we find that NovA converges significantly more rapidly than standard $N$-body, producing little or no spurious halos on small scales. We show, however, that determining whether or not halos exist below the free streaming mass $M_{\rm fs}$ is complicated by the fact that our halo finder (AHF) likely incorrectly labels some caustics and criss-crossing filaments as halos, while one or two particularly massive filaments appear to fragment in any version of NovA where refinement is allowed. Such massive filaments may be physically unstable to collapse, as is the case for infinite, static, self-gravitating cylinders. We will use NovA in forthcoming papers to study the issue of halo formation below $M_{\rm fs}$; filament stability; and to obtain new constraints on the temperature of dark matter.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
