10 MK gas in M17 and the Rosette Nebula: X-ray flows in galactic HII regions

We present the first high spatial resolution X-ray images of two high-mass star forming regions, the Omega Nebula (M17) and the Rosette Nebula (NGC 2237-2246), obtained with the Chandra X-Ray Observatory Advanced CCD Imaging Spectrometer instrument. The massive clusters powering these H II regions are resolved at the arcsecond level into more than 900 (M17) 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 is spatially and spectrally distinct from the point-source population. The diffuse emission has luminosity L-X similar or equal to 3.4 x 10(33) ergs s(-1) in M17 with plasma energy components at kT similar or equal to 0.13 and similar or equal to0.6 keV (1.5 and 7 MK), while in Rosette it has L-X similar or equal to 6 x 10(32) ergs s(-1) with plasma energy components at kT similar or equal to 0.06 and similar or equal to0.8 keV (0.7 and 9 MK). This extended emission most likely arises from the fast O star winds thermalized either by wind-wind collisions or by a termination shock against the surrounding media. We establish that only a small portion of the wind energy and mass appears in the observed diffuse X-ray plasma; in these blister H II regions, we suspect that most of it flows without cooling into the low-density interstellar medium. These data provide compelling observational evidence that strong wind shocks are present in H II regions.