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

Abstract

We present the first high-spatial-resolution X-ray images of two high-mass star forming regions, the Omega Nebula (M 17) and the Rosette Nebula (NGC 2237(NGC -2246, obtained with the Chandra X-ray Observatory Advanced CCD Imaging Spectrometer (ACIS) instrument. The massive clusters powering these HII regions 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 is spatially and spectrally distinct from the point source population. The diffuse emission has luminosity L x ≃ 3.4 × 10 33 ergs s −1 in M 17 with plasma energy components at kT ≃ 0.13 and ≃ 0.6 keV (1.5 and 7 MK), while in Rosette it has L x ≃ 6 × 10 32 ergs s −1 with plasma energy components at kT ≃ 0.06 and ≃ 0.8 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 HII 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 HII regions.

The outburst decay of the low magnetic field magnetar SWIFT J1822.3−1606: phase-resolved analysis and evidence for a variable cyclotron feature

“…Using the best 1(T-fixed)+2(free) BB model and the whole set of phase-average spectra, we obtained a best-fit column density value of NH = 4.7(1) × 10 21 cm −2 , which is very close to the values found in previous works, R12 NH = 5.0(1) × 10 21 cm −2 ; and Scholz et al (2012) NH = 4.5(1)×10 21 cm −2 . Moreover, this value is consistent with the NH = 4(1) × 10 21 cm −2 of the Galactic HII region M17 (Townsley et al 2003), located about 20 ′ from Swift J1822 and at 1.6 ± 0.3 kpc from us (Nielbock et al 2001), as noted by Scholz et al (2012). We kept NH fixed at 4.7 × 10 21 cm −2 for the rest of the analysis, and adopted a tentative distance of 1.6 kpc in BB radii calculations.…”

Using population synthesis of massive stars to study the interstellar medium near OB associations

“…The flow of wind and supernova ejecta inside cavities can be very complex (MacLow et al 2005), and the propagation is likely dominated by turbulent diffusion from magnetic field irregularities caused by the stellar winds and supernovae Parizot 2004). Part of the gas will be thermalized near the stellar association due to wind-wind collisions or by a termination shock against the turbulent medium inside the cavity, and this can be observed as a hot X-ray emitting plasma (Townsley et al 2003;Güdel et al 2008). However the majority of the mass will expand into the low density cavity.…”

Star formation history of Canis Major R1

“…In particular, following up on pioneering ROSAT observations, intermediate to distant clouds have been covered by Chandra: the Orion nebula (Garmire et al 2000;Feigelson et al 2002Feigelson et al , 2003Flaccomio et al 2003), part of the Rosette nebula and molecular cloud, together with M17 (Townsley et al 2003;Wang et al 2008Wang et al , 2009); Mon R2 (Kohno et al 2002); RCW38 (Wolk et al 2002); M16 (Linsky et al 2007), and by XMMNewton: M8 (Rauw et al 2002); Carina (Albacete Colombo et al 2003); Vela OB2 (Jeffries et al 2009); Orion (López-Santiago & Caballero 2008); and others. Up to thousands of point X-ray sources per cloud are detected, almost all identified with young stars, down to the brown dwarf regime.…”

“…Alternatively, Reynolds & Ogden (1978) proposed that the nebula and star formation were induced by strong stellar winds, or by an evolving, "fossil" HII region, as also suggested by Blitz (1980) and Pyatunina & Taraskin (1986). However, because they are found to be in pressure equilibrium with the parent molecular cloud once they have opened a cavity (see the example of M 17, Townsley et al 2003;or Orion, Güdel et al 2008), stellar winds cannot compress the surrounding medium and induce star formation. On the other hand, we now know many examples of HII "bubbles" apparently triggering star formation near their edges (e.g., Deharveng et al 2008;Zavagno et al 2007), but these bubbles have well-defined exciting stars.…”