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Fast magnetic field amplification in distant galaxy clusters
Nature Astronomy ( IF 14.1 ) Pub Date : 2020-11-02 , DOI: 10.1038/s41550-020-01244-5
Gabriella Di Gennaro , Reinout J. van Weeren , Gianfranco Brunetti , Rossella Cassano , Marcus Brüggen , Matthias Hoeft , Timothy W. Shimwell , Huub J. A. Röttgering , Annalisa Bonafede , Andrea Botteon , Virginia Cuciti , Daniele Dallacasa , Francesco de Gasperin , Paola Domínguez-Fernández , Torsten A. Enßlin , Fabio Gastaldello , Soumyajit Mandal , Mariachiara Rossetti , Aurora Simionescu

In the present-day Universe, magnetic fields pervade galaxy clusters1 and have strengths of a few microgauss, as measured from Faraday rotation2. Evidence for cluster magnetic fields is also provided by the observation of megaparsec-scale radio emission, namely radio halos and relics3. These are commonly found in merging systems4 and are characterized by a steep radio spectrum Sν (α < −1, where Sν να and is ν the observing frequency). It is widely believed that magneto-hydrodynamical turbulence and shock waves (re-)accelerate cosmic rays5 and produce radio halos and relics. The origin and amplification of magnetic fields in clusters is not well understood. It has been proposed that turbulence drives a small-scale dynamo6,7,8,9,10,11 that amplifies seed magnetic fields (which are primordial and/or injected by galactic outflows, such as active galactic nuclei, starbursts or winds12). At high redshift, radio halos are expected to be faint, owing to losses from inverse Compton scattering and the dimming effect with distance. Moreover, Faraday rotation measurements are difficult to obtain. If detected, distant radio halos provide an alternative tool to investigate magnetic field amplification. Here, we report Low Frequency Radio Array observations that reveal diffuse radio emission in massive clusters when the Universe was only half of its present age, with a sample occurrence fraction of about 50%. The high radio luminosities indicate that these clusters have similar magnetic field strengths to those in nearby clusters, and suggest that magnetic field amplification is fast during the first phases of cluster formation.



中文翻译:

遥远星系团中的快速磁场放大

在当今的宇宙中,磁场自法拉第旋转2以来,遍及星系团1并具有几微高斯的强度。兆秒级规模的无线电发射,即无线电晕和文物3的观测,也提供了簇磁场的证据。这些通常在融合系统中发现的4和由一个陡峭的无线电频谱的特征在于小号να <1,其中小号ν α ν α并且是ν观察频率)。人们普遍认为,磁流体动力湍流和冲击波(重新)加速了宇宙射线5 并产生无线电晕和文物。簇中磁场的起源和放大还没有被很好地理解。有人提出,湍流驱动小型发电机6,7,8,9,10,11放大种子磁场(原始磁场和/或由银河外流注入的磁场,例如活跃的银河核,星爆或风12)。)。在高红移下,由于因康普顿逆散射和随距离变暗的影响而造成的损失,无线电晕会变得微弱。此外,法拉第旋转测量值很难获得。如果检测到,遥远的无线电晕将为研究磁场放大提供另一种工具。在这里,我们报告了低频无线电阵列观测结果,这些发现揭示了宇宙只有现今年龄的一半时,大规模星团中的漫射无线电发射,样本发生率约为50%。高射电发光度表明这些星团具有与附近星团相似的磁场强度,并表明在星团形成的第一阶段,磁场放大很快。

更新日期:2020-11-02
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