Origin of Galactic Spurs: New Insight from Radio/X-ray All-sky Maps

TL;DR

This paper investigates the origins of giant Galactic spurs seen in radio and X-ray all-sky maps, revealing their physical differences and suggesting they result from past Galactic explosions and local star formation activities.

Contribution

It provides new insights into the physical origins and spatial offsets of Galactic spurs, linking them to halo gas dynamics and Galactic activity history.

Findings

X-ray emissions from NPS and SPS are closer to the Galactic center than radio emissions.

LAS offsets are larger and attributed to different physical processes.

X-ray temperatures of LAS are lower, consistent with halo gas temperatures.

Abstract

In this study, we analyze giant Galactic spurs seen in both radio and X-ray all-sky maps to reveal their origins. We discuss two types of giant spurs: one is the brightest diffuse emission near the map's center, which is likely to be related to Fermi bubbles (NPSs/SPSs, north/south polar spurs, respectively), and the other is weaker spurs that coincide positionally with local spiral arms in our Galaxy (LAS, local arm spur). Our analysis finds that the X-ray emissions, not only from the NPS but from the SPS are closer to the Galactic center by ~5 deg compared with the corresponding radio emission. Furthermore, larger offsets of 10-20 deg are observed in the LASs; however, they are attributed to different physical origins. Moreover, the temperature of the X-ray emission is kT ~ 0.2 keV for the LAS, which is systematically lower than those of the NPS and SPS (kT ~ 0.3 keV) but consistent with the typical temperature of Galactic halo gas. We argue that the radio/X-ray offset and the slightly higher temperature of the NPS/SPS X-ray gas are due to the shock compression/heating of halo gas during a significant Galactic explosion in the past, whereas the enhanced X-ray emission from the LAS may be due to the weak condensation of halo gas in the arm potential or star formation activity without shock heating.