X-Ray Emission Signatures of Galactic Feedback in the Hot Circumgalactic Medium: Predictions from Cosmological Hydrodynamical Simulations

Abstract Little is currently known about the physical properties of the hot circumgalactic medium (CGM) surrounding massive galaxies. Next-generation X-ray observatories will enable detailed studies of the hot CGM in emission. To support these future efforts, we make predictions of the X-ray emission from the hot CGM using a sample of 28 ∼Milky Way-mass disk galaxies at z = 0 from seven cosmological hydrodynamical simulation suites incorporating a wide range of galactic feedback prescriptions. The X-ray surface brightness (XSB) morphology of the hot CGM varies significantly across simulations. XSB-enhanced outflows and bubble-like structures are predicted in many galaxies simulated with active galactic nuclei (AGN) feedback and in some stellar-feedback-only galaxies, while other galaxies exhibit more isotropic XSB distributions at varying brightnesses. Galaxies simulated without cosmic-ray physics exhibit radial XSB profiles with similar shapes (∝ r −3 within 20–200 kpc), with scatter about this slope likely due to underlying feedback physics. The hot CGM kinematics also differ substantially: velocity maps reveal signatures of bulk CGM rotation and high-velocity biconical outflows, particularly in simulations incorporating AGN feedback. Some stellar-feedback-only models also generate similar AGN-like outflows, which we postulate is due to centrally concentrated star formation. Simulations featuring AGN feedback frequently produce extended temperature enhancements in large-scale galactic outflows, while simulations incorporating cosmic-ray physics predict the coolest CGM due to pressure support being provided by cosmic rays rather than hot CGM. Individually resolved X-ray emission lines further distinguish hot CGM phases, with lower-energy lines (e.g., O VII ) largely tracing volume-filling gas, and higher-energy lines (e.g., Fe XVII ) highlighting high-velocity feedback-driven outflows.