44 GHz Class I Methanol (CH$_{3}$OH) Maser Survey in the Galactic Center

Abstract

We report on a large 44 GHz ($7_0-6_1$ A$^+$) methanol (CH$_3$OH) maser survey of the Galactic Center (GC). The Karl G. Jansky Very Large Array was used to search for CH$_3$OH maser emission covering a large fraction of the region around Sgr A. In 25 pointings, over 300 CH$_3$OH maser sources ($>10\sigma$) were detected. The majority of the maser sources have a single peak emission spectrum with line of sight velocities that range from about $-$13 km\,s$^{-1}$ to 72 km\,s$^{-1}$. Most maser sources were found to have velocities around 35$-$55 km\,s$^{-1}$, closely following velocities of neighboring interacting molecular clouds. The full width half maximum of each individual spectral feature is very narrow ($\sim$0.85 km\,s$^{-1}$ on average). In the north, where Sgr A East is known to be interacting with the 50 km\,s$^{-1}$ molecular cloud, more than 100 44 GHz CH$_3$OH masers were detected. In addition, three other distinct concentrations of masers were found, which appear to be located closer to the interior of the interacting molecular clouds. Possibly a subset of masers are associated with star formation, although conclusive evidence is lacking.