Are the observed outflow gas phases manifestations of a single phenomenon or unrelated events?

Determine whether the multi-phase gaseous outflows observed in active galactic nuclei—including hot ionized, warm ionized, neutral atomic, and molecular components—are different manifestations of a single outflow phenomenon with phase transitions between components, or whether these phases represent unrelated events.

Background

Observations report outflows across multiple gas phases (hot ionized, warm ionized, neutral atomic, and molecular) spanning from sub-parsec to kiloparsec scales. Although multi-phase properties have been measured in some cases, most studies provide single-phase estimates, leaving an incomplete view of the global mass and energy budget of outflows.

This uncertainty motivates establishing whether these phases are physically connected through phase transitions within the same outflow, or whether they arise from unrelated processes. Clarifying this point is essential for accurately assessing feedback energetics and the impact of outflows on star formation and galaxy evolution.

References

From the observational point of view it is not clear yet whether the different outflow phases are different faces of the same phenomenon, with certain phases transitioning to others , or just unrelated events.

— Observational Tests of Active Galactic Nuclei Feedback: An Overview of Approaches and Interpretation  (2404.08050 - Harrison et al., 2024) in Section 4.1 (Multi-phase gas outflows)

The physical relationship between the high-latitude (mostly UV-traced) and the low-latitude (mostly -traced) clouds remains unclear.

— High Velocity Neutral Gas in the Fermi Bubbles: New Kinematic Limits and Spatial Structure  (2608.16754 - Lockman et al., 17 Aug 2026) in Section 3.1, “Related results from UV spectroscopy”