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arXiv 2407.14596astro-ph.GAastro-ph.HEphysics.plasm-ph
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z=5.6 星系中千秒差距尺度的有序磁场

A kiloparsec-scale ordered magnetic field in a galaxy at z=5.6

Jianhang Chen, Enrique Lopez-Rodriguez, R. J. Ivison, James E. Geach, Simon Dye, Xiaohui Liu, George Bendo

AI总结:

本文通过对 z=5.6 的强透镜尘埃恒星形成星系 SPT0346-52 进行静止系 131 μm 全偏振观测,发现其具有千秒差距尺度有序磁场,并揭示其结构与冷气体运动及并合过程相关。

摘要:

磁场在各种天文环境中被广泛观测到,但关于其在不同系统和宇宙时期中的重要性,仍有许多未知。我们目前对磁场演化的认识受到遥远宇宙中观测稀缺的限制;而在遥远宇宙中,近期发现星系比大多数模型预测更为演化。为填补这一空白,我们对 z=5.6、即宇宙年龄仅为 1 Gyr 时的强引力透镜尘埃恒星形成星系 SPT0346-52 中的尘埃发射进行了静止系 131 μm 全偏振观测。尘埃颗粒可与局地磁场排列,从而产生线偏振热红外辐射。我们的观测揭示,在 3 kpc 的延伸范围内,中位偏振水平为 0.9±0.2%,变化幅度为 ±0.4%,表明存在大尺度有序磁场。偏振尘埃发射呈斑块状,相对于总尘埃发射发生偏移,并主要与速度约为 -150 km/s 的 [C II] 发射重叠。磁场方向的双峰分布、其空间分布以及与冷气体运动学的联系,进一步强调了该星系磁环境的复杂性,以及并合在塑造其磁场方面的潜在作用。这种有序星系磁场的早期形成还表明,小尺度和大尺度发电机在早期星系中都可能是高效的。继续观测早期星系中的磁场,并将巡天扩展到更广泛的星系群体,对于全面认识磁场在演化宇宙中的普遍性和影响至关重要。

英文摘要:

Magnetic fields are widely observed in various astronomical contexts, yet much remains unknown about their significance across different systems and cosmic epochs. Our current knowledge of the evolution of magnetic fields is limited by scarce observations in the distant Universe, where galaxies have recently been found to be more evolved than most model predictions. To address this gap, we conducted rest-frame 131 um full-polarisation observations of dust emission in a strongly lensed dusty star-forming galaxy, SPT0346-52, at z=5.6, when the Universe was only 1 Gyr old. Dust grains can become aligned with local magnetic fields, resulting in the emission of linearly polarised thermal infrared radiation. Our observations have revealed a median polarisation level of $0.9\pm0.2$ percent with a variation of $\pm0.4$ percent across the 3 kpc extention, indicating the presence of large-scale ordered magnetic fields. The polarised dust emission is patchy, offset from the total dust emission and mostly overlaps with the [C II] emission at a velocity of about -150 km/s. The bimodal distribution of field orientations, their spatial distribution, and the connection with the cold gas kinematics further emphasise the complexity of the magnetic environment in this galaxy and the potential role of mergers in shaping its magnetic fields. Such early formation of ordered galactic magnetic fields also suggests that both small-scale and large-scale dynamos could be efficient in early galaxies. Continued observations of magnetic fields in early galaxies, as well as expanding surveys to a wider galaxy population, are essential for a comprehensive understanding of the prevalence and impact of magnetic fields in the evolving Universe.

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