桥接邦迪和事件视界尺度：3D GRMHD模拟揭示X形射电星系形态
Bridging Bondi and Event Horizon Scales: 3D GRMHD Simulations Reveal X-Shaped Radio Galaxy Morphology
摘要：
X形射电星系（XRGs）产生错位的X形喷流对，构成射电星系的$\lesssim10\%$。XRG被认为出现在具有超大质量双黑洞（$\rm SMBH$）、$\rm SMBH$合并或大尺度环境介质不对称的星系中。我们证明，XRG形态可以自然形成，没有这种特殊的，预先存在的条件。我们的3D广义相对论磁流体动力学（GRMHD）模拟第一次遵循磁化旋转气体从半径$R_{\rm B}$的$\rm SMBH$影响球到引力半径$R_{\rm g}$的$\rm SMBH$，在迄今为止最大的尺度分离$R_{\rm B}/R_{\rm g} = 10^3$。最初，我们的轴对称系统的恒定密度的热气体包含弱的垂直磁场和旋转的赤道平面的快速旋转$\rm SMBH$。我们用小规模的$2\%$水平的压力扰动来播种气体。进入的气体形成一个吸积盘，$\rm SMBH$发射出相对论磁化的准直喷流，到达$R_{\rm B}$的外部。在下落气体的压力下，射流间歇地打开和关闭，不规则地摆动，并在不同方向上膨胀成对的空腔，类似于X形射流形态。合成X射线图像显示了多对喷气动力冲击和空腔。大规模的磁通量积累在$\rm SMBH$上，变得动态重要，并导致磁制动盘状态。$\rm SMBH$以邦迪速率的$2\%$（M87* 为$\dot{M}\simeq2.4\times10^{-3}M_{\odot}\,{\rm yr}^{-1}$）吸积，并以$η=150\%$效率发射双喷流。这些喷流足够强大（$P_{\rm jets}\simeq2\times10^{44}\,{\rm erg\,s}^{-1}$），可以沿着自旋轴逃逸，并结束短暂的喷流状态，其瞬态性质可以解释XRG的罕见性
英文摘要：
X-shaped radio galaxies (XRGs) produce misaligned X-shaped jet pairs and make up $\lesssim10\%$ of radio galaxies. XRGs are thought to emerge in galaxies featuring a binary supermassive black hole ($\rm SMBH$), $\rm SMBH$ merger, or large-scale ambient medium asymmetry. We demonstrate that XRG morphology can naturally form without such special, preexisting conditions. Our 3D general-relativistic magnetohydrodynamic (GRMHD) simulation for the first time follows magnetized rotating gas from outside the $\rm SMBH$ sphere of influence of radius $R_{\rm B}$ to the $\rm SMBH$ of gravitational radius $R_{\rm g}$, at the largest scale separation $R_{\rm B}/R_{\rm g} = 10^3$ to date. Initially, our axisymmetric system of constant-density hot gas contains weak vertical magnetic field and rotates in an equatorial plane of a rapidly spinning $\rm SMBH$. We seed the gas with small-scale $2\%$-level pressure perturbations. Infalling gas forms an accretion disk, and the $\rm SMBH$ launches relativistically-magnetized collimated jets reaching well outside $R_{\rm B}$. Under the pressure of the infalling gas, the jets intermittently turn on and off, erratically wobble, and inflate pairs of cavities in different directions, resembling an X-shaped jet morphology. Synthetic X-ray images reveal multiple pairs of jet-powered shocks and cavities. Large-scale magnetic flux accumulates on the $\rm SMBH$, becomes dynamically important, and leads to a magnetically arrested disk state. The $\rm SMBH$ accretes at $2\%$ of the Bondi rate ($\dot{M}\simeq2.4\times10^{-3}M_{\odot}\,{\rm yr}^{-1}$ for M87*), and launches twin jets at $η=150\%$ efficiency. These jets are powerful enough ($P_{\rm jets}\simeq2\times10^{44}\,{\rm erg\,s}^{-1}$) to escape along the spin axis and end the short-lived jets state whose transient nature can account for the rarity of XRGs
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