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arXiv 1008.3530astro-ph.CO
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星系团A2255的深部多频旋转测量层析成像

Deep multi-frequency rotation measure tomography of the galaxy cluster A2255

R. F. Pizzo, A. G. de Bruyn, G. Bernardi, M. A. Brentjens

摘要:

我们的目标是通过WSRT在18、21、25、85和200 cm处的观测揭示Abell 2255的三维几何结构。通过旋转测量(RM)合成处理团簇的偏振图像,产生三个最终的RM立方体。射电星系和晕边缘的丝状体是在高频RM立方体中探测到的,该立方体是通过结合18、21和25厘米处的数据获得的。它们的法拉第光谱显示出不同程度的复杂性。位于星系团中心附近的射电星系的法拉第谱有多个峰,而距离较远的射电星系只有一个峰,灯丝也是如此。观测到外部射电星系和暗条星系的RM分布相似,但其平均RM值和RM方差远低于以往中央射电星系的观测结果。85厘米的RM立方体主要是由银河系前景发射,但它也显示出与集群相关的功能。在2米处,没有检测到来自A2255和我们银河系的偏振辐射。在射电星系的RM分布和它们的法拉第光谱的复杂性中观察到的径向趋势有利于解释A2255中所有源的外部法拉第屏是ICM。它的差分贡献取决于无线电信号沿视线穿过的介质的数量。因此,暗条应该位于星系团的外围,它们明显的中心位置来自投影效应。它们的高分数极化和形态表明它们是遗迹,而不是真正的射电晕的一部分。他们推断的大距离集群中心和他们的几何形状可以争辩与大尺度结构(LSS)的冲击。

英文摘要:

We aim to unveil their 3-dimensional geometry of Abell 2255 through WSRT observations at 18, 21, 25, 85, and 200 cm. The polarization images of the cluster were processed through rotation measure (RM) synthesis, producing three final RM cubes. The radio galaxies and the filaments at the edges of the halo are detected in the high-frequency RM cube, obtained by combining the data at 18, 21, and 25 cm. Their Faraday spectra show different levels of complexity. The radio galaxies lying near by the cluster center have Faraday spectra with multiple peaks, while those at large distances show only one peak, as do the filaments. Similar RM distributions are observed for the external radio galaxies and for the filaments, with much lower average RM values and RM variance than those found in previous works for the central radio galaxies. The 85 cm RM cube is dominated by the Galactic foreground emission, but it also shows features associated with the cluster. At 2 m, no polarized emission from A2255 nor our Galaxy is detected. The radial trend observed in the RM distributions of the radio galaxies and in the complexity of their Faraday spectra favors the interpretation that the external Faraday screen for all the sources in A2255 is the ICM. Its differential contribution depends on the amount of medium that the radio signal crosses along the line of sight. The filaments should therefore be located at the periphery of the cluster, and their apparent central location comes from projection effects. Their high fractional polarization and morphology suggest that they are relics rather than part of a genuine radio halo. Their inferred large distance from the cluster center and their geometry could argue for an association with large-scale structure (LSS) shocks.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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