Thermal generation of cosmological seed magnetic fields in ionization fronts
Thermal generation of cosmological seed magnetic fields in ionization fronts
复制标题
电离前沿宇宙种子磁场的热生成
DOI：
10.1093/mnras/271.1.l15
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发表时间：
1994
影响因子：
4.8
通讯作者：
S. Chitre
中科院分区：
文献类型：
--
作者：
K. Subramanian;D. Narasimha;S. Chitre
类星体光谱表明星系际介质（IGM）在红移z≥ 5时被再电离，可能是由于类星体和年轻星系等电离光子的离散源。在这种情况下，电离前沿将远离这些源扩展，直到它们渗透并包围IGM的大部分。作用于电子的电离前沿中的压力梯度可以导致热生成的电场。这个场将有一个非零的旋度，因此意味着一个不断增长的磁场，前提是前部的压力梯度不平行于密度梯度。这种情况在宇宙学背景下自然会出现，因为IGM包含原始（增长）密度波动，其密度梯度与由任意放置的电离源产生的压力梯度无关。在这个过程中，磁场可以在IGM的很大一部分上热生成。特别是，它们在银河系尺度上的强度约为3 × 10-20 G，并且可以作为种子场，供银河发电机进一步放大。
Quasar spectra indicate that the intergalactic medium (IGM) was reionized at some redshift z≥ 5, probably due to discrete sources of ionizing photons like QSOs and young galaxies. In such a circumstance, ionization fronts will expand away from these sources until they percolate and encompass a substantial part of the IGM. The pressure gradients in the ionization front acting on electrons can lead to a thermally generated electric field. This field will have a non-vanishing curl and hence imply a growing magnetic field, provided the pressure gradient in the front is not parallel to the density gradient. Such a situation obtains naturally in the cosmological context because the IGM harbours primordial (growing) density fluctuations whose density gradients are not correlated with the pressure gradients produced by an arbitrarily placed ionizing source. In this process, magnetic fields can be thermally generated, over a good fraction of the IGM. In particular, they can have strengths ~3 × 10-20 G on galactic scales, and can serve as seed fields for further amplification by the galactic dynamo.