FR II radio galaxies at low frequencies - II. Spectral ageing and source dynamics
FR II radio galaxies at low frequencies - II. Spectral ageing and source dynamics
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低频 FR II 射电星系 - II。
DOI：
10.1093/mnras/stx820
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发表时间：
2017
影响因子：
4.8
通讯作者：
Harwood J
中科院分区：
文献类型：
--
作者：
Harwood J
在本文中，第二个在一系列调查法那罗夫-莱利II型（FR II）射电星系在低频率，我们使用低频阵列（LOFAR）和甚大阵（VLA）的观测117和456 MHz之间，除了档案数据，以确定两个射电星系，3C 452和3C 223的动力学和能量学，通过在小空间尺度上拟合光谱老化模型。我们提供了改进的测量的物理范围内的两个来源，包括以前未知的低表面亮度扩展到北方瓣的3C 223，并根据这些值修订能量。我们发现3C 452和3C 223的光谱年龄分别为0.05和0.05万年，这表明波瓣的特征前进速度约为光速的1%。对于3C 452，我们表明，即使磁场强度不假设是均分，一个差距的一个因素约为2之间存在的光谱年龄和从动力学的角度来看，确定。我们确认，这两个源的注入指数（来自波瓣发射）仍然比经典假设的值陡峭，即使在低频下考虑良好的分辨率尺度。然而，我们发现了一个意想不到的尖锐的热点和周围的波瓣发射的频谱之间的不连续性。我们认为，这种差异是热点发射和/或非均匀和额外的加速机制的吸收的结果，因此，热点不应该被用于确定潜在的初始电子能量分布。
In this paper, the second in a series investigating Fanaroff–Riley type II (FR II) radio galaxies at low frequencies, we use LOw Frequency ARray (LOFAR) and Very Large Array (VLA) observations between 117 and 456 MHz, in addition to archival data, to determine the dynamics and energetics of two radio galaxies, 3C 452 and 3C 223, by fitting spectral ageing models on small spatial scales. We provide improved measurements for the physical extent of the two sources, including a previously unknown low surface brightness extension to the northern lobe of 3C 223, and revised energetics based on these values. We find spectral ages ofandMyr for 3C 452 and 3C 223, respectively, suggesting a characteristic advance speed for the lobes of around 1 per cent of the speed of light. For 3C 452, we show that, even for a magnetic field strength not assumed to be in equipartition, a disparity of a factor of approximately 2 exists between the spectral age and that determined from a dynamical standpoint. We confirm that the injection index of both sources (as derived from the lobe emission) remains steeper than classically assumed values, even when considered on well-resolved scales at low frequencies. However, we find an unexpected sharp discontinuity between the spectrum of the hotspots and the surrounding lobe emission. We suggest that this discrepancy is a result of the absorption of hotspot emission and/or non-homogeneous and additional acceleration mechanisms; as such, hotspots should not be used in the determination of the underlying initial electron energy distribution.