模拟X形射电星系：来自回流模型的动力学和发射特征
Modelling X-shaped Radio Galaxies: Dynamical and Emission Signatures from the Back-flow model
摘要：
一些射电星系的喷流出现扭曲，形成有尾或有翼的源。X型射电星系是有翼源的一个子类，其形成机制至今仍不清楚。这项工作的重点是了解流体动力学回流和它们的作用，在动力学和非热发射签名（在存在的辐射损失和扩散冲击加速）在这些星系的初始阶段。我们已经进行了相对论MHD模拟的密度不足的射流在三轴环境中使用混合欧拉-拉格朗日框架，将微物理过程的影响。我们已经证明了在热主导的情况下，压力梯度在塑造XRG中发挥的主导作用。我们发现，突出的形成的结构减少射流偏离的主轴环境。机翼的演变主要是由重新通电的粒子由于冲击，保持结构在演变期间活跃。射电星系的合成强度图显示出与通常在观测到的XRG中发现的形态相似。这包括具有比活动叶更宽的翼的情况。本文还讨论了它的同步辐射特征和均分条件在年龄估算中的意义。此外，我们表明，年龄的差异可以归因于不同年龄的粒子群的混合。此外，视角对活动瓣和翼$(Δα)$的光谱指数差的影响显示出大的变化和退化行为。我们已经证明了扩散冲击的作用，在所获得的变化，并得出结论，传播的$(Δα)$是不是一个可靠的特点，在确定的XRG的形成模式。
英文摘要：
Some of the radio galaxies show distortion in their jets, forming tailed or winged sources. X-shaped radio galaxies are a subclass of winged sources formation mechanism of which is still unclear. The focus of this work is to understand hydro-dynamical back-flows and their role in dynamics and non-thermal emission signatures (in presence of radiative losses and diffusive shock acceleration) during the initial phase of these galaxies. We have performed relativistic MHD simulations of an under-dense jet travelling in a tri-axial ambient using a hybrid Eulerian-Lagrangian framework to incorporate effects of micro-physical processes. We have demonstrated the dominant role played by pressure gradient in shaping XRGs in thermally dominated cases. We show that the prominence of the formed structure decreases as the jet deviates from the major axis of the ambient. The wing evolution is mainly governed by re-energized particles due to shocks that keep the structure active during the evolution time. The synthetic intensity maps of the radio galaxy show similarities with morphologies that are typically found in observed XRGs. This includes the cases with wider wings than the active lobes. The characteristic emission signatures in terms of its synchrotron spectra and implication of equipartition condition in age estimation are also discussed here. Additionally, we show that discrepancy of age can be attributed to mixing of different aged particle populations. Further, the effect of viewing angle on the difference of spectral index of the active lobes and the wings $(Δα)$ shows a large variation and degenerate behaviour. We have demonstrated the role of diffusive shocks in the obtained variation and have concluded that the spread of $(Δα)$ is not a dependable characteristic in determining the formation model of XRGs.
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