Galactic winds and bubbles from nuclear starburst rings

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.