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

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 also from the SPS, are closer to the Galactic center by similar to 5 degrees compared with the corresponding radio emission. Furthermore, larger offsets of 10 degrees-20 degrees 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.

Automated summary

This study analyzes the origins and characteristics of giant Galactic spurs, finding offsets between X-ray and radio emissions which may be due to shock compression and heating of halo gas during a significant Galactic explosion in the past. The enhanced X-ray emission from local arm spurs may be caused by weak condensation of halo gas in the arm potential or star formation activity without shock heating.