The RMS Survey: Ammonia and water maser analysis of massive star forming regions

TL;DR

This study used the Green Bank telescope to analyze ammonia and water maser emissions in about 600 massive young stellar objects, revealing correlations between gas properties, maser activity, and stellar luminosity, advancing understanding of massive star formation.

Contribution

First comprehensive ammonia and water maser survey of ~600 RMS sources, establishing key correlations between gas properties, maser activity, and stellar luminosity in massive star forming regions.

Findings

High detection rate of ammonia (~80%) indicates dense gas presence.

Strong correlation between maser velocities and ammonia emission suggests association.

Luminosity correlates with gas temperature, line width, and maser luminosity.

Abstract

The Red MSX Source (RMS) survey has identified a sample of ~1200 massive young stellar objects (MYSOs), compact and ultra compact HII regions from a sample of ~2000 MSX and 2MASS colour selected sources. We have used the 100 m Green Bank telescope to search for 22-24 GHz water maser and ammonia (1,1), (2,2) and (3,3) emission towards ~600 RMS sources located within the northern Galactic plane. We have identified 308 H2O masers which corresponds to an overall detection rate of ~50%. Abridged: We detect ammonia emission towards 479 of these massive young stars, which corresponds to ~80%. Ammonia is an excellent probe of high density gas allowing us to measure key parameters such as gas temperatures, opacities, and column densities, as well as providing an insight into the gas kinematics. The average kinetic temperature, FWHM line width and total NH3 column density for the sample are approximately 22 K, 2 km/s and 2x10^{15} cm^{-2}, respectively. We find that the NH3 (1,1) line width and kinetic temperature are correlated with luminosity and finding no underlying dependence of these parameters on the evolutionary phase of the embedded sources, we conclude that the observed trends in the derived parameters are more likely to be due to the energy output of the central source and/or the line width-clump mass relationship. The velocities of the peak H2O masers and the NH3 emission are in excellent agreement with each other, which would strongly suggest an association between the dense gas and the maser emission. Moreover, we find the bolometric luminosity of the embedded source and the isotropic luminosity of the H2O maser are also correlated. We conclude from the correlations of the cloud and water maser velocities and the bolometric and maser luminosity that there is a strong dynamical relationship between the embedded young massive star and the H2O maser.