Thursday, July 25, 2013

1307.6473 (Paula Benaglia et al.)

High resolution radio emission from RCW 49/Westerlund 2    [PDF]

Paula Benaglia, Baerbel Koribalski, Cintia S. Peri, Josep Marti, Juan R. Sanchez-Sutil, Sean M. Dougherty, Alberto Noriega-Crespo
The HII region RCW 49 and its ionizing cluster form an extensive, complex region that has been widely studied at infrared and optical wavelengths. Molonglo 843 MHz and ATCA data at 1.4 and 2.4 GHz showed two shells. Recent high-resolution IR images revealed a complex dust structure and ongoing star formation. New high-bandwidth and high-resolution data of the RCW 49 field have been obtained to survey the radio emission at arcsec scale and investigate the small-scale features and nature of the HII region. Radio observations were collected with the new 2-GHz bandwidth receivers and the ATCA CABB correlator, at 5.5 and 9.0 GHz. In addition, archival observations at 1.4 and 2.4 GHz have been re-reduced and re-analyzed in conjunction with observations in the optical, infrared, X-ray and gamma-ray regimes.- The new 2-GHz bandwidth data result in the most detailed radio continuum images of RCW 49 to date. The radio emission closely mimics the near-IR emission observed by Spitzer, showing pillars and filaments. The brightest continuum emission is in the region known as the 'bridge'. Optically thin thermal emission is expected to be detected, but there are hints that non-thermal emission may be present in the bridge. A number of discrete sources have been detected in the surroundings of RWC 49, along with two apparent bow shocks and a jet-like structure surrounded by a ring. Only one of these sources appears associated with a known stellar source.- The radio results support an association between the ionized plasma detected at radio wavelengths with the molecular gas in the region, with a kinematic distance of the bridge of 6 - 7 kpc. For the case that the negative spectral indices measured of the bridge are due to synchrotron emission, we propose a scenario where high energy emission is produced. The jet-like structure appears as an intriguing source that deserves a detailed study by its own.
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