Galactic winds and bubbles from nuclear starburst rings

TL;DR

This paper uses 3D simulations to show how starburst rings can produce layered galactic winds with hot and cool phases, resembling observed structures like the Milky Way's bubbles, without needing external confinement.

Contribution

It introduces a novel model of energy-driven winds from starburst rings that naturally explains multi-phase galactic outflows and their collimation without magnetic or pressure confinement.

Findings

Hot winds shock and maintain high temperatures within the ring.

Unobstructed flows cool rapidly to form cooler outflows.

Wind velocities can reach those typical of AGN-driven winds.

Abstract

Galactic outflows from local starburst galaxies typically exhibit a layered geometry, with cool $10^4\,$K flow sheathing a hotter $10^7\,$K, cylindrically-collimated, X-ray emitting plasma. Here, we argue that winds driven by energy-injection in a ring-like geometry can produce this distinctive large-scale multi-phase morphology. The ring configuration is motivated by the observation that massive young star clusters are often distributed in a ring at the host galaxy's inner Lindblad resonance, where larger-scale spiral arm structure terminates. We present parameterized three-dimensional radiative hydrodynamical simulations that follow the emergence and dynamics of energy-driven hot winds from starburst rings. In this Letter, we show that the flow shocks on itself within the inner ring hole, maintaining high $10^7$\,K temperatures, whilst flows that emerge from the wind-driving ring unobstructed can undergo rapid bulk cooling down to $10^4\,$K, producing a fast hot bi-conical outflow enclosed by a sheath of cooler nearly co-moving material without ram-pressure acceleration. The hot flow is collimated along the ring axis, even in the absence of pressure confinement from a galactic disk or magnetic fields. In the early stages of expansion, the emerging wind forms a bubble-like shape reminiscent of the Milky Way's eROSITA and Fermi bubbles and can reach velocities usually associated with AGN-driven winds. We discuss the physics of the ring configuration, the conditions for radiative bulk cooling, and the implications for future X-ray observations.