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

Abstract

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 (CMZ). These observations detect thermal emission from cold ISM dust, thermal free-free emission from ionized gas, and nonthermal synchrotron emission from relatively flat-spectrum sources. Archival data sets spanning $3.6\mu$m to 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 though 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${}^{\circ }$, with a mean 2 mm spectral index which is steeper than at longer wavelengths. The 2 mm to 6 cm (or 20 cm) spectral index steepens from $\alpha \approx -0.2$ 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 $21^{\prime \prime }$) 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.

arXiv comment17 pages, 11 figures. Accepted for publication in the ApJ

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Cited by in corpus (7)

• Statistical Properties of the Population of the Galactic Center Filaments: The Spectral Index and Equipartition Magnetic Field
• The Atacama Cosmology Telescope: Microwave Intensity and Polarization Maps of the Galactic Center
• The Population of the Galactic Center Filaments: Position Angle Distribution Reveal a Degree-scale Collimated Outflow from Sgr A* along the Galactic Plane
• Populations of Magnetized Filaments in the Intracluster Medium and the Galactic Center
• Statistical Properties of the Population of the Galactic Center Filaments II: The Spacing Between Filaments
• 2 mm GISMO Observations of the Galactic Center. I. Dust Emission
• 6.7 GHz CH3OH absorption towards the N3 Galactic Center point-source