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 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.
