The circumgalactic medium (CGM) encodes signatures of the galaxy-formation process, including the interaction of galactic outflows driven by stellar and supermassive black hole (SMBH) feedback with the gaseous halo. Moving beyond spherically symmetric radial profiles, we study the angular dependence of CGM properties around z = 0 massive galaxies in the IllustrisTNG simulations. We characterize the angular signal of density, temperature, and metallicity of the CGM as a function of galaxy stellar mass, halo mass, distance, and SMBH mass, via stacking. TNG predicts that the CGM is anisotropic in its thermodynamical properties and chemical content over a large mass range, $M_*\sim 10^{10-11.5}\, \mathrm{M}_\odot$. Along the minor axis directions, gas density is diluted, whereas temperature and metallicity are enhanced. These feedback-induced anisotropies in the CGM have a magnitude of 0.1−0.3 dex, extend out to the halo virial radius, and peak at Milky Way-like masses, $M_*\sim 10^{10.8}\, \mathrm{M}_\odot$. In TNG, this mass scale corresponds to the onset of efficient SMBH feedback and the production of strong outflows. By comparing the anisotropic signals predicted by TNG versus other simulations – Illustris and EAGLE – we find that each simulation produces distinct signatures and mass dependencies, implying that this phenomenon is sensitive to the underlying physical models. Finally, we explore X-ray emission as an observable of this CGM anisotropy, finding that future X-ray observations, including the eROSITA all-sky survey, will be able to detect and characterize this signal, particularly in terms of an angular modulation of the X-ray hardness.

中文翻译：

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环银河介质中各向异性 X 射线特征的预测：超大质量黑洞驱动外流的印记

环银河介质 (CGM) 编码了星系形成过程的特征，包括由恒星和超大质量黑洞 (SMBH) 反馈驱动的星系外流与气态晕的相互作用。超越球对称径向剖面，我们研究了 IllustrisTNG 模拟中 z = 0 大质量星系周围 CGM 特性的角度依赖性。我们通过叠加将 CGM 的密度、温度和金属丰度的角信号表征为星系恒星质量、晕质量、距离和 SMBH 质量的函数。TNG 预测 CGM 的热力学性质和化学成分在很大的质量范围内是各向异性的，$M_*\sim 10^{10-11.5}\,\mathrm{M}_\odot$。沿短轴方向，气体密度被稀释，而温度和金属丰度提高。CGM 中这些由反馈引起的各向异性的大小为 0.1−0.3 dex，延伸到光晕维里半径，并在类似银河系的质量处达到峰值，$M_*\sim 10^{10.8}\,\mathrm{M }_\dot$。在 TNG 中，这种大规模对应于有效 SMBH 反馈的开始和强烈流出的产生。通过将 TNG 预测的各向异性信号与其他模拟（Illustris 和 EAGLE）进行比较，我们发现每个模拟都会产生不同的特征和质量依赖性，这意味着这种现象对基础物理模型很敏感。最后，我们探索 X 射线发射作为这种 CGM 各向异性的可观测值，发现未来的 X 射线观测，包括 eROSITA 全天调查，将能够检测和表征该信号，特别是在角度调制方面X 射线硬度。