Small-scale Dynamo in Supernova-driven Interstellar Turbulence,The Astrophysical Journal Letters

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Small-scale Dynamo in Supernova-driven Interstellar Turbulence
The Astrophysical Journal Letters ( IF 8.8 ) Pub Date : 2021-03-31 , DOI: 10.3847/2041-8213/abed59
Frederick A. Gent _{1,

2} , Mordecai-Mark Mac Low _{3,

4} , Maarit J. Kpyl _{1,

5,

6} , Nishant K. Singh _{5,

7}

Affiliation

Magnetic fields grow quickly even at early cosmological times, suggesting the action of a small-scale dynamo (SSD) in the interstellar medium of galaxies. Many studies have focused on idealized turbulent driving of the SSD. Here we simulate more realistic supernova-driven turbulence to determine whether it can drive an SSD. Magnetic field growth occurring in our models appears inconsistent with simple tangling of magnetic fields, but consistent with SSD action, reproducing and confirming models by Balsara et al. that did not include physical resistivity η. We vary η, as well as the numerical resolution and supernova rate, $\dot{\sigma }$ , to delineate the regime in which an SSD occurs. For a given $\dot{\sigma }$ we find convergence for SSD growth rate with resolution of a parsec. For $\dot{\sigma }\simeq {\dot{\sigma }}_{\mathrm{sn}}$ , with ${\dot{\sigma }}_{\mathrm{sn}}$ the solar neighborhood rate, the critical resistivity below which an SSD occurs is $0.005\gt {\eta }_{\mathrm{crit}}\gt 0.001\,\mathrm{kpc}\,\mathrm{km}\,{{\rm{s}}}^{-1}$ , and this increases with the supernova rate. Across the modeled range of 0.5–4pc resolution we find that for $\eta \lt {\eta }_{\mathrm{crit}}$ , the SSD saturates at about 5% of kinetic energy equipartition, independent of growth rate. In the range $0.2\,{\dot{\sigma }}_{\mathrm{sn}}\leqslant \dot{\sigma }\leqslant 8\,{\dot{\sigma }}_{\mathrm{sn}}$ growth rate increases with $\dot{\sigma }$ . SSDs in the supernova-driven interstellar medium commonly exhibit erratic growth.

中文翻译：

超新星驱动的星际湍流中的小规模发电机

即使在宇宙学早期，磁场也会快速增长，这表明星系的星际介质中存在小型发电机 (SSD) 的作用。许多研究都集中在 SSD 的理想化湍流驱动上。这里我们模拟更真实的超新星驱动湍流，以确定它是否可以驱动 SSD。在我们的模型中发生的磁场增长似乎与磁场的简单缠结不一致，但与 SSD 动作一致，重现和确认了 Balsara 等人的模型。不包括物理电阻率η。我们改变η以及数值分辨率和超新星率 $\dot{\sigma }$ ，以描绘 SSD 发生的区域。对于给定的情况， $\dot{\sigma }$ 我们发现 SSD 增长率与解析度的收敛性。为了 $\dot{\sigma }\simeq {\dot{\sigma }}_{\mathrm{sn}}$ ，随着 ${\dot{\sigma }}_{\mathrm{sn}}$ 太阳邻域率，发生 SSD 的临界电阻率为 $0.005\gt {\eta }_{\mathrm{crit}}\gt 0.001\,\mathrm{kpc}\,\mathrm{km}\,{{\rm{s}}}^{-1}$ ，并且随着超新星率的增加而增加。在 0.5-4pc 分辨率的建模范围内，我们发现对于 $\eta \lt {\eta }_{\mathrm{crit}}$ ，SSD 在动能均分的 5% 左右饱和，与增长率无关。在该范围内， $0.2\,{\dot{\sigma }}_{\mathrm{sn}}\leqslant \dot{\sigma }\leqslant 8\,{\dot{\sigma }}_{\mathrm{sn}}$ 增长率随增加 $\dot{\sigma }$ 。超新星驱动的星际介质中的固态硬盘通常表现出不稳定的增长。

更新日期：2021-03-31

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