低频射电星系FR II I：形态、磁场强度和能量
FR II radio galaxies at low frequencies I: morphology, magnetic field strength and energetics
摘要：
由于其陡峭的光谱，FR II射电星系的低频观测可能提供这些强大的射电源的形态，能量和光谱的关键见解。然而，上一代无线电干涉仪在米波长上的局限性意味着这一参数空间区域在很大程度上仍未得到探索。在本文中，第一个在一系列检查FR II在低频，我们使用LOFAR观测50和160 MHz之间，随着补充档案无线电和X射线数据，探索两个FR II源，3C 452和3C 223的属性。我们发现，3C 452的形态是一个标准的FR II，而不是一个双双射电星系，如以前所建议的，没有剩余的发射被观察到超出了活动叶。我们发现，这两个源的低频综合光谱比传统假设的预期陡得多，并使用同步加速器/逆康普顿模型拟合，表明叶的总能量含量大于以前的估计约5倍的3C 452和2 3C 223。我们继续讨论可能的原因，这些陡峭的光谱比预期的，并提供修订后的内部压力和磁场强度的固有陡峭的情况下的估计。我们发现，均分磁场强度和那些来自通过同步/逆康普顿模型拟合之间的比率仍然与以前的研究结果一致，并表明，所观察到的偏离均分可能在某些情况下提供了一个解决方案的光谱与动力学年龄差距。
英文摘要：
Due to their steep spectra, low-frequency observations of FR II radio galaxies potentially provide key insights in to the morphology, energetics and spectrum of these powerful radio sources. However, limitations imposed by the previous generation of radio interferometers at metre wavelengths has meant that this region of parameter space remains largely unexplored. In this paper, the first in a series examining FR IIs at low frequencies, we use LOFAR observations between 50 and 160 MHz, along with complementary archival radio and X-ray data, to explore the properties of two FR II sources, 3C452 and 3C223. We find that the morphology of 3C452 is that of a standard FR II rather than of a double-double radio galaxy as had previously been suggested, with no remnant emission being observed beyond the active lobes. We find that the low-frequency integrated spectra of both sources are much steeper than expected based on traditional assumptions and, using synchrotron/inverse-Compton model fitting, show that the total energy content of the lobes is greater than previous estimates by a factor of around 5 for 3C452 and 2 for 3C223. We go on to discuss possible causes of these steeper than expected spectra and provide revised estimates of the internal pressures and magnetic field strengths for the intrinsically steep case. We find that the ratio between the equipartition magnetic field strengths and those derived through synchrotron/inverse-Compton model fitting remains consistent with previous findings and show that the observed departure from equipartition may in some cases provide a solution to the spectral versus dynamical age disparity.
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