The physical and chemical structure of Sagittarius B2. V. Non-thermal emission in the envelope of Sgr B2
Journal
Date Issued
2019
Author(s)
Meng, F.
•
Sánchez-Monge, Á.
•
Schilke, P.
•
•
Marcowith, A.
•
Ginsburg, A.
•
Schmiedeke, A.
•
Schwörer, A.
•
DePree, C.
•
Veena, V. S.
•
Möller, Th.
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).
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.
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.
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.
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.
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.
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.
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.
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.
Funding(s)
Volume
630
Start page
A73
Issn Identifier
0004-6361
Ads BibCode
2019A&A...630A..73M
Rights
open.access
File(s)![Thumbnail Image]()
![Thumbnail Image]()
Loading...
Name
1908.07237.pdf
Description
postprint
Size
2.75 MB
Format
Adobe PDF
Checksum (MD5)
a858a481c85dfbc88e06e3a3deb61fe3
Loading...
Name
aa35920-19.pdf
Description
Pdf editoriale
Size
3.15 MB
Format
Adobe PDF
Checksum (MD5)
e89d3b1f50dd81bc936675eb7e0c6d6b