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D. Wang (UMass), R. Walterbos (NMSU), D. Thilker (NRAO), R. Broun (NFfRA)
We present a multiwavelength study of the face-on galaxy M101. We detect expanding hot superbubbles using a 3-D HI data cube, an FUV observation, and a deep X-ray imaging. The kinetic energy of the detected superbubbles are comparable to the thermal energy of their enclosed X-ray-emitting gas, consistent with the hypothesis that they are driven by supernovae and stellar winds from massive stars. The superbubbles are typically associated with young giant HII regions and dynamically much older than the regions, indicating the propagation of star formation. Furthermore, some of the HII regions are apparently mass-loading the superbubbles, which may explain the bright X-ray emission of these superbubbles. We find that X-ray emission correlates strongly with spiral arms and with HII regions in general. This suggests that massive stars in the galaxy are primarily responsible for the X-ray-emitting gas with a characteristic temperature of a few times 106~K. The blown out of this very hot gas from the galactic disk, can naturally explain an apparently cooler halo gas component of about 106~K within the central 5 kpc radius of the galaxy.
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