Determine the nature of the Perseus bay structure

Determine whether the bay structure in the southern Perseus arm is a fossil active-galactic-nucleus cavity or a Kelvin–Helmholtz instability in a sloshing cold front, thereby identifying the mechanism responsible for the associated metal-abundance and velocity enhancements.

Background

The southern arm contains a bay structure located between the third and fourth radial regions. The paper identifies two competing interpretations: the rim or wake of an ancient AGN-inflated bubble, or a Kelvin–Helmholtz instability generated in a sloshing cold front.

The measured abundance enhancement, velocity dispersion, and velocity shear are compatible with either scenario. The authors explicitly state that their observations do not distinguish between them and call for additional observations and theoretical work.