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Paper: Sagittarius B2: Understanding the Mix of Thermal and Non-thermal Emission
Volume: 528, New Horizons in Galactic Center Astronomy and Beyond
Page: 317
Authors: Meng, F.; Sánchez-Monge, Á.; Schilke, P.; Veena, V. S.
Abstract: The giant molecular cloud Sagittarius B2 (hereafter SgrB2) is the most massive region with ongoing high-mass star formation in the Galaxy. In the southern region of the 20-pc large envelope of SgrB2, we encounter the SgrB2(DS) region which hosts more than 60 high-mass proto-stellar cores distributed in an arc shape around an extended HII region. We use the Very Large Array in its CnB and D configurations, and in the frequency bands C (4–8 GHz) and X (8–12 GHz) to observe the whole SgrB2 complex. Continuum and radio recombination line maps are obtained. We detect radio continuum emission in SgrB2(DS) in a bubble-shaped structure. Using data from 4 to 12 GHz, we derive a spectral index between -1.2 and -0.4, indicating the presence of non-thermal emission. The radio recombination lines in the region are found to be not in local thermodynamic equilibrium (LTE) but stimulated by the non-thermal emission. The thermal free-free emission is likely tracing the HII region ionized by an O7 star, while the non-thermal emission can be generated by the relativistic electrons created through first-order Fermi acceleration.
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