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|Title:||The physical and chemical structure of Sagittarius B2. V. Non-thermal emission in the envelope of Sgr B2||Authors:||Meng, F.
Veena, V. S.
|Issue Date:||2019||Journal:||ASTRONOMY & ASTROPHYSICS||Number:||630||First Page:||A73||Abstract:||Context. The giant molecular cloud Sagittarius B2 (hereafter Sgr B2) is the most massive region with ongoing high-mass star formation in the Galaxy. In the southern region of the 40-pc large envelope of Sgr B2, we encounter the Sgr B2(DS) region, which hosts more than 60 high-mass protostellar cores distributed in an arc shape around an extended H II region. Hints of non-thermal emission have been found in the H II region associated with Sgr B2(DS). <BR /> Aims: We seek to characterize the spatial structure and the spectral energy distribution of the radio continuum emission in Sgr B2(DS). We aim to disentangle the contribution from the thermal and non-thermal radiation, as well as to study the origin of the non-thermal radiation. <BR /> Methods: We used 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 Sgr B2 complex. Continuum and radio recombination line maps are obtained. <BR /> Results: We detect radio continuum emission in Sgr B2(DS) in a bubble-shaped structure. From 4 to 12 GHz, we derive a spectral index between - 1.2 and - 0.4, indicating the presence of non-thermal emission. We decomposed the contribution from thermal and non-thermal emission, and find that the thermal component is clumpy and more concentrated, while the non-thermal component is more extended and diffuse. The radio recombination lines in the region are found to be not in local thermodynamic equilibrium but stimulated by the non-thermal emission. <BR /> Conclusions: Sgr B2(DS) shows a mixture of thermal and non-thermal emission at radio wavelengths. The thermal free-free emission is likely tracing an H II region ionized by an O 7 star, while the non-thermal emission can be generated by relativistic electrons created through first-order Fermi acceleration. We have developed a simple model of the Sgr B2(DS) region and found that first-order Fermi acceleration can reproduce the observed flux density and spectral index.||URI:||http://hdl.handle.net/20.500.12386/28678||URL:||https://www.aanda.org/articles/aa/full_html/2019/10/aa35920-19/aa35920-19.html||ISSN:||0004-6361||DOI:||10.1051/0004-6361/201935920||Bibcode ADS:||2019A&A...630A..73M||Fulltext:||open|
|Appears in Collections:||1.01 Articoli in rivista|
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