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)

While the cooler phases are easier to observe, it remains unclear if these observations alone are sufficient to describe the entire multiphase outflow.

— Studying Outflows with Synthetic Absorption Line Spectra from High Resolution Simulations  (2609.10868 - Magee et al., 9 Sep 2026) in Section 1, Introduction

These absorbers indicate that different ionisation and velocity components may be physically connected, although a common origin for all WAs and UFOs remains unestablished.

— AGN winds and outflows: from accretion-disc scales to the host galaxy  (2609.29758 - Porquet, 24 Sep 2026) in Section 1, subsection “The X-ray view of ionised AGN winds”

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”

This may mean that the wind dissipates within the inner few kiloparsecs or that the optical phase traces only a small fraction of a multiphase outflow whose larger mass and energy budget are carried by atomic and molecular gas. Without radio--millimeter observations, however, this remains uncertain.

— Super-Eddington Accretion and Early-Stage Feedback in Ton S180  (2609.04317 - Condò et al., 3 Sep 2026) in Section 6.3, “Feedback from the nucleus to kiloparsec scales”

It is possible that our assumption of a continuous outflow that results in a continuous AMD is wrong, and these are two separate outflows.

— Stratified Wind Geometries of GRS 1915+105: Density Profiles and Radii  (2609.08731 - Keshet et al., 8 Sep 2026) in Discussion, paragraph beginning “The density and launch radius”

Whether the nuclear ionized outflow has a cold-gas counterpart at these velocities therefore cannot be tested with the present data and requires further observations.

— A dust-reddened quasar in a [C II]-luminous host at z=6.55  (2610.13758 - Yang et al., 9 Oct 2026) in Section 3.4, “C II emission and dust continuum”