2 mm GISMO Observations of the Galactic Center. II. A Nonthermal Filament in the Radio Arc and Compact Sources

We have used the Goddard IRAM 2 Millimeter Observer (GISMO) with the 30 m IRAM telescope to carry out a 2 mm survey of the Galaxy’s central molecular zone. These observations detect thermal emission from cold interstellar medium dust, thermal free–free emission from ionized gas, and nonthermal synch...

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Bibliographic Details
Published in:The Astrophysical journal 2019-11, Vol.885 (1), p.72
Main Authors: Staguhn, Johannes, Arendt, Richard G., Dwek, Eli, Morris, Mark. R., Yusef-Zadeh, Farhad, Benford, Dominic J., Kovacs, Attila, Gonzalez-Quiles, Junellie
Format: Article
Language:English
Subjects:
Astronomy
Astrophysics
Dust
Dust emission
Filaments
Galaxies
H II regions
Interstellar chemistry
Interstellar gas
Interstellar matter
Interstellar medium
Molecular clouds
Morphology
Point sources
Radio
Thermal emission
Wavelengths
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Summary:We have used the Goddard IRAM 2 Millimeter Observer (GISMO) with the 30 m IRAM telescope to carry out a 2 mm survey of the Galaxy’s central molecular zone. These observations detect thermal emission from cold interstellar medium dust, thermal free–free emission from ionized gas, and nonthermal synchrotron emission from relatively flat-spectrum sources. Archival data sets spanning 3.6 μm–90 cm are used to distinguish different emission mechanisms. After the thermal emission of dust is modeled and subtracted, the remaining 2 mm emission is dominated by free–free emission, with the exception of the brightest nonthermal filament (NTF) that runs through the middle of the bundle of filaments known as the Radio Arc. This is the shortest wavelength at which any NTF has been detected. The GISMO observations clearly trace this NTF over a length of ∼0°. 2, with a mean 2 mm spectral index that is steeper than at longer wavelengths. The 2 mm–6 cm (or 20 cm) spectral index steepens from α ≈ −0.2 to −0.7 as a function distance from the Sickle H II region, suggesting that this region is directly related to the NTF. A number of unresolved (at 21″) 2 mm sources are found nearby. One appears to be thermal dust emission from a molecular cloud that is associated with an enigmatic radio point source whose connection to the Radio Arc is still debated. The morphology and colors at shorter IR wavelengths indicate other 2 mm unresolved sources are likely to be compact H II regions.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/ab451b