Letter to the Editor

North Polar Spur: Gaseous plume(s) from star-forming regions ∼3–5 kpc from the Galactic Center?

¹ Max Planck Institute for Astrophysics, Karl-Schwarzschild-Str. 1, D-85741 Garching, Germany
² Space Research Institute (IKI), Profsoyuznaya 84/32, Moscow 117997, Russia
³ Universitäts-Sternwarte, Fakultät für Physik, Ludwig-Maximilians-Universität München, Scheinerstr. 1, 81679 München, Germany
⁴ Ioffe Institute, Politekhnicheskaya St. 26, Saint Petersburg 194021, Russia
⁵ Institute of Astronomy, Russian Academy of Sciences, 48 Pyatnitskaya Str., Moscow 119017, Russia
⁶ NRC ‘Kurchatov Institute’, Acad. Kurchatov Square 1, Moscow 123182, Russia
⁷ Institute of Applied Physics of the Russian Academy of Sciences, 46 Ul’yanov Str., Nizhny Novgorod 603950, Russia

^⋆ Corresponding author; churazov@mpa-garching.mpg.de

Received: 1 August 2024
Accepted: 31 October 2024

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 the 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 speeds 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.