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

TL;DR

This study conducted a large survey of 44 GHz methanol masers in the Galactic Center, detecting over 300 sources and analyzing their velocities and distribution, revealing insights into molecular cloud interactions and potential star formation regions.

Contribution

First large-scale 44 GHz methanol maser survey in the Galactic Center, providing detailed source counts, velocity profiles, and spatial distribution insights.

Findings

Over 300 maser sources detected with narrow spectral features.

Most masers have velocities around 35-55 km/s, matching molecular clouds.

Significant maser concentration near Sgr A East and molecular clouds.

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.