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 \sim 0.2 \arcdeg , 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 \ion H2 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 \ion H2 regions .