AI 中文总结
该研究利用低频阵列对阿贝尔2255星系团进行超深场观测，通过同步辐射强度梯度技术研究其磁场拓扑结构至质心半径，发现磁场在不同区域有优先取向，首次展示围绕星系团从核心到边缘的连贯大尺度磁场拓扑，凸显低频观测对探测磁场结构的独特作用。
AI 中文摘要
我们展示了低频阵列星系团超深场，其中在附近（红移\(z = 0.080\)）的阿贝尔2255星系团上收集了336小时120 - 168兆赫兹的低频阵列观测数据。这个庞大且正在合并的系统以星系团星系和星系团内介质发出的壮观射电辐射而闻名。之前的低频阵列观测揭示了从星系团中心延伸到其动态活跃边缘的普遍弥漫同步辐射，追踪在大尺度磁场中传播的相对论电子。在这项工作中，我们基于224小时最佳质量数据，呈现了一组中心频率为144兆赫兹的新超深图像，在7.1”×4.3”分辨率下达到24微焦耳每束的灵敏度。这些图像代表了迄今为止对星系团最深的射电观测，并让我们得以一窥在不久的将来用低频阵列低频段常规观测星系团时的景象。利用这些数据，我们通过应用同步辐射强度梯度技术研究了星系团磁场拓扑结构延伸至其质心半径的情况。我们发现推断出的磁场在星系团的不同区域呈现出优先取向，比如在射电晕延伸部分（桥）和遗迹中，这表明星系团形成过程的动力学正在塑造大尺度磁场。与宇宙磁流体动力学模拟得到的磁场取向进行比较支持了这一解释。这项工作首次表明了在整个星系团从核心到边缘存在连贯的大尺度磁场拓扑结构，并展示了超深低频观测在追踪百万秒差距尺度上星系团磁场结构从而探测宇宙大尺度结构磁化方面的独特能力。
英文摘要
We present the LOFAR Galaxy Cluster Ultra-Deep Field, in which 336 h of LOFAR observations at 120$-$168 MHz have been collected on the nearby ($z=0.080$) cluster Abell 2255. This massive and merging system is known to host spectacular radio emission from both cluster galaxies and the intracluster medium. Previous LOFAR observations revealed pervasive diffuse synchrotron emission extending from the cluster center to its dynamically active outskirts, tracing relativistic electrons propagating in large-scale magnetic fields. In this work, we present a set of new ultra-deep images at the central frequency of 144 MHz based on the 224 h of data with the best quality, which reach a sensitivity of 24 $μ$Jy beam$^{-1}$ at 7.1" $\times$ 4.3" resolution. These images represent the deepest radio observations of a galaxy cluster obtained to date and provide a glimpse of what should be routinely observed in clusters with SKA-Low in the near future. Using these data, we investigate the topology of the cluster magnetic field out to its virial radius by applying the synchrotron intensity gradient technique. We find that the inferred magnetic field exhibits preferential orientations in distinct regions of the cluster, such as in the radio halo extensions (bridges) and in the relics, suggesting that the dynamics of the cluster formation process is shaping the large-scale magnetic field. This interpretation is supported by the comparison with the magnetic field orientation obtained from cosmological magnetohydrodynamic simulations. This work provides the first indication of a coherent, large-scale magnetic field topology across an entire galaxy cluster, from core to outskirts, and demonstrates the unique power of ultra-deep, low-frequency observations to trace the structure of cluster magnetic fields on megaparsec scales, thereby probing the magnetization of the large-scale structure of the Universe.
Comments15 pages, 10 figures + Appendix. Accepted for publication in A&A
