Energy Partition in Active Galactic Nucleus-driven Bubbles of NGC 4438: From Nuclear Bubbles to a Galaxy-scale Outflow

This is the authors' abstract. We don't add key points for this paper.

Jets launched by accreting supermassive black holes represent a major mode of active galactic nucleus (AGN) feedback. However, how their energy is divided among bulk kinetic motion, thermal gas, magnetic fields, cosmic rays, and radiation—and how this distribution changes with spatial scale—remains poorly constrained. NGC 4438 provides a unique laboratory for probing this evolution, hosting two 200 pc scale nuclear bubbles and a lopsided ∼10 kpc galaxy-scale outflow plausibly associated with the same AGN. We present a multiwavelength analysis to investigate the morphology, radiation mechanisms, and energetics of these structures. Joint radio—X-ray modeling shows that the nonthermal emission in the nuclear bubbles may require two distinct populations of cosmic-ray electrons, suggesting that in addition to shock acceleration at the bubble rim, the highest-energy particles may be linked to acceleration processes closer to the unresolved central engine. A spatially resolved energy inventory reveals that bulk kinetic energy dominates the current energy budget of the nuclear bubbles, while roughly half of the injected energy has already been transformed into thermal, cosmic ray, and magnetic energy, as well as radiative losses. Across all bubble sizes, the thermal and magnetic pressures are consistent within the uncertainties, implying that magnetic fields remain dynamically significant on all examined spatial scales. Furthermore, the empirical correlation between radio luminosity and jet power, established for kiloparsec-scale jet bubbles, matches the energetics of the galaxy-scale outflow but substantially overestimates the power of the 200 pc-scale nuclear bubbles, underscoring the scale dependence of jet energy dissipation.