A Large--Scale Spectroscopic Survey of Methanol and OH Line Emission from the Galactic Center: Observations and Data

TL;DR

This paper presents a comprehensive VLA survey of methanol and OH masers in the Galactic Center, cataloging thousands of masers with high spatial resolution and analyzing their potential association with star formation and infrared dark clouds.

Contribution

It provides the largest catalog of methanol and OH masers in the Galactic Center with detailed spectral and spatial data, offering insights into their origins and relation to star formation.

Findings

Cataloged 2240 methanol masers with narrow linewidths.

Detected 23 OH (1612), 14 OH (1665), 5 OH (1667), and 5 OH (1720) masers.

Many methanol masers are associated with infrared dark clouds, but not all trace early star formation.

Abstract

Class I methanol masers are collisionally pumped and are generally correlated with outflows in star forming sites in the Galaxy. Using the VLA in its A-array configuration, we present a spectral line survey to identify methanol $J=4_{-1}\rightarrow3_0E$ emission at 36.169~GHz. Over 900 pointings were used to cover a region 66'x13'along the inner Galactic plane. A shallow survey of OH at 1612, 1665, 1667 and 1720 MHz was also carried out over the area covered by our methanol survey. We provide a catalog of 2240 methanol masers with narrow line-widths of $\sim1$ km s$^{-1}$, spatial resolution of ~0.14"x0.05" and RMS noise $\sim20$ mJy beam$^{-1}$ per channel. Lower limits on the brightness temperature range from 27,000 K to 10,000,000 K showing the emission is of non-thermal origin. We also provide a list of 23 OH (1612), 14 OH (1665), 5 OH (1667) and 5 OH(1720 MHz) masers. The origin of such a large number of methanol masers is not clear. Many methanol masers appear to be associated with infrared dark clouds, though it appears unlikely that the entire population of masers trace early phase of star formation in the Galactic center.