Dynamo coefficients from local simulations of the turbulent ISM

被引:46
作者
Gressel, O. [1 ]
Ziegler, U. [1 ]
Elstner, D. [1 ]
Ruediger, G. [1 ]
机构
[1] Astrophys Inst Potsdam, D-14482 Potsdam, Germany
关键词
ISM : supernova remnants; magnetohydrodynamics (MHD); magnetic fields; turbulence;
D O I
10.1002/asna.200811005
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
Observations in polarized emission reveal the existence of large-scale coherent magnetic fields in a wide range of spiral galaxies. Radio-polarization data show that these fields are strongly inclined towards the radial direction, with pitch angles up to 35 degrees and thus cannot be explained by differential rotation alone. Global dynamo models describe the generation of the radial magnetic field from the underlying turbulence via the so called a-effect. However, these global models still rely on crude assumptions about the small-scale turbulence. To overcome these restrictions we perform fully dynamical MHD simulations of interstellar turbulence driven by supernova explosions. From our simulations we extract profiles of the contributing diagonal elements of the dynamo alpha-tensor as functions of galactic height. We also measure the coefficients describing vertical pumping and find that the ratio between these two effects has been overestimated in earlier analytical work, where dynamo action seemed impossible. In contradiction to these models based on isolated remnants we always find the pumping to be directed inward. In addition we observe that depends on whether clustering in terms of super-bubbles is taken into account. Finally, we apply a test field method to derive a quantitative measure of the turbulent magnetic diffusivity which we determine to be similar to 2 kpc km s(-1) (c) 2008 WILEY-VCH Verlag GmbH & Co. KGaA. Weinheim
引用
收藏
页码:619 / 624
页数:6
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