The Arecibo Methanol Maser Galactic Plane Survey - III: Distances and Luminosities

TL;DR

This study determines distances and luminosities of 86 methanol masers in the Galactic plane, revealing their distribution and estimating the maser population in nearby galaxies.

Contribution

It provides the first comprehensive kinematic distance measurements and luminosity function for 6.7 GHz methanol masers in the Milky Way.

Findings

Most sources are at the far kinematic distance.

The vertical distribution has a scale height of ~30 pc.

The maser luminosity function peaks at ~10^{-6} L_sun.

Abstract

We derive kinematic distances to the 86 6.7 GHz methanol masers discovered in the Arecibo Methanol Maser Galactic Plane Survey. The systemic velocities of the sources were derived from 13CO (J=2-1), CS (J=5-4), and NH3 observations made with the ARO Submillimeter Telescope, the APEX telescope, and the Effelsberg 100 m telescope, respectively. Kinematic distance ambiguities were resolved using HI self-absorption with HI data from the VLA Galactic Plane Survey. We observe roughly three times as many sources at the far distance compared to the near distance. The vertical distribution of the sources has a scale height of ~ 30 pc, and is much lower than that of the Galactic thin disk. We use the distances derived in this work to determine the luminosity function of 6.7 GHz maser emission. The luminosity function has a peak at approximately 10^{-6} L_sun. Assuming that this luminosity function applies, the methanol maser population in the Large Magellanic Cloud and M33 is at least 4 and 14 times smaller, respectively, than in our Galaxy.