10 MK Gas in M17 and the Rosette Nebula: X‐Ray Flows in Galactic HiiRegions

We present the first high-spatial-resolution X-ray images of two high-massstar forming regions, the Omega Nebula (M 17) and the Rosette Nebula (NGC2237--2246), obtained with the Chandra X-ray Observatory Advanced CCD ImagingSpectrometer (ACIS) instrument. The massive clusters powering these H IIregions are resolved at the arcsecond level into >900 (M 17) and >300 (Rosette)stellar sources similar to those seen in closer young stellar clusters.However, we also detect soft diffuse X-ray emission on parsec scales that isspatially and spectrally distinct from the point source population. The diffuseemission has luminosity L_x ~ 3.4e33 ergs/s in M~17 with plasma energycomponents at kT ~0.13 and ~0.6 keV (1.5 and 7 MK), while in Rosette it has L_x\~6e32 ergs/s with plasma energy components at kT ~0.06 and ~0.8 keV (0.7 and 9MK). This extended emission most likely arises from the fast O-star windsthermalized either by wind-wind collisions or by a termination shock againstthe surrounding media. We establish that only a small portion of the windenergy and mass appears in the observed diffuse X-ray plasma; in these blisterH II regions, we suspect that most of it flows without cooling into thelow-density interstellar medium. These data provide compelling observationalevidence that strong wind shocks are present in H II regions.Comment: 35 pages, including 11 figures; to appear in ApJ, August 20, 2003. A version with high-resolution figures is available at ftp://ftp.astro.psu.edu/pub/townsley/diffuse.ps.g