North Polar Spur: gaseous plume(s) from star-forming regions at $\sim$3-5 kpc from Galactic Center?

TL;DR

This paper proposes that the North Polar Spur and similar structures are formed by metal-rich gaseous plumes from star-forming regions at 3-5 kpc from the Galactic Center, shaped by buoyancy and rotation effects.

Contribution

It introduces a model linking star-forming regions to the formation and morphology of the North Polar Spur through buoyant gaseous plumes.

Findings

Plumes originate from star-forming regions at 3-5 kpc from the Galactic Center.

Plumes acquire bent shapes due to differential rotation and buoyancy.

Model reproduces observed radio and X-ray structures.

Abstract

We argue that the North Polar Spur (NPS) and many less prominent structures are formed by gaseous metal-rich plumes associated with star-forming regions (SFRs). The SFRs located at the tangent to the 3-5~kpc rings might be particularly relevant to NPS. A multi-temperature mixture of gaseous components and cosmic rays rises above the Galactic disk under the action of their initial momentum and buoyancy. Eventually, the plume velocity becomes equal to that of the ambient gas, which rotates with different angular speed than the stars in the disk. As a result, the plumes acquire characteristic bent shapes. An ad hoc model of plumes' trajectories shows an interesting resemblance to the morphology of structures seen in the radio continuum and X-rays.