The Red MSX Source survey: ammonia and water maser analysis of massive star-forming regions★

Abstract

The Red MSX Source (RMS) survey has identified a sample of ~1200 massive\nyoung stellar objects (MYSOs), compact and ultra compact HII regions from a\nsample of ~2000 MSX and 2MASS colour selected sources. We have used the 100 m\nGreen Bank telescope to search for 22-24 GHz water maser and ammonia (1,1),\n(2,2) and (3,3) emission towards ~600 RMS sources located within the northern\nGalactic plane. We have identified 308 H2O masers which corresponds to an\noverall detection rate of ~50%. Abridged: We detect ammonia emission towards\n479 of these massive young stars, which corresponds to ~80%. Ammonia is an\nexcellent probe of high density gas allowing us to measure key parameters such\nas gas temperatures, opacities, and column densities, as well as providing an\ninsight into the gas kinematics. The average kinetic temperature, FWHM line\nwidth and total NH3 column density for the sample are approximately 22 K, 2\nkm/s and 2x10^{15} cm^{-2}, respectively. We find that the NH3 (1,1) line width\nand kinetic temperature are correlated with luminosity and finding no\nunderlying dependence of these parameters on the evolutionary phase of the\nembedded sources, we conclude that the observed trends in the derived\nparameters are more likely to be due to the energy output of the central source\nand/or the line width-clump mass relationship. The velocities of the peak H2O\nmasers and the NH3 emission are in excellent agreement with each other, which\nwould strongly suggest an association between the dense gas and the maser\nemission. Moreover, we find the bolometric luminosity of the embedded source\nand the isotropic luminosity of the H2O maser are also correlated. We conclude\nfrom the correlations of the cloud and water maser velocities and the\nbolometric and maser luminosity that there is a strong dynamical relationship\nbetween the embedded young massive star and the H2O maser.\n