Diffuse X-ray emission on the Cygnus OB2 association

ALBACETE COLOMBO, J. F; DRAKE, J. J.; FLACCOMIO, E.; KASHYAP, V.; GUARCELLO, M.; WRIGHT, N. J.

ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES

IOP PUBLISHING LTD

Lugar: Londres; Año: 2018

0067-0049

We present a large-scale study of diffuse X-ray emission in the nearby massive stellar association CygnusOB2 as part of the Chandra Cygnus OB2 Legacy Program. We used 40 Chandra X-ray ACIS-I observationscovering ∼1.0 deg 2 . After removing 7924 point-like sources detected in our survey, background-correctedX-ray emission, the adaptive smoothing reveals large-scale diffuse X-ray emission. Diffuse emission was de-tected in the sub-bands Soft [0.5 : 1.2] and Medium [1.2 : 2.5], and marginally in the Hard [2.5 : 7.0] keV band.From X-ray spectral analysis of stacked spectra we compute a total [0.5-7.0 keV] diffuse X-ray luminosity ofL diff≈4.2×10 34 erg s −1 , characterized with plasma temperature components at kT≈ 0.11, 0.40 and 1.18 keV,xrespectively. The Hi absorption column density corresponding to these temperatures has a distribution consis-tent with N H = 0.43, 0.80 and 1.39 ×10 22 cm −2 . The extended medium band energy emission likely arises fromO-type stellar winds thermalized by wind-wind collisions in the most populated regions of the association,while the soft band emission probably arises from less energetic termination shocks against the surroundingInterstellar-Medium. Super-soft and Soft diffuse emission appears more widely dispersed and intense thanthe medium band emission. The diffuse X-ray emission is generally spatially coincident with low-extinctionregions that we attribute to the ubiquitous influence of powerful stellar winds from massive stars and theirinteraction with the local Interstellar-Medium. Diffuse X-ray emission is volume-filling, rather than edge-brightened, oppositely to other star-forming regions. We reveal the first observational evidence of X-ray haloesaround some evolved massive stars.