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 young stellar objects (MYSOs), compact and ultra-compact H II regions from a sample of ∼2000 MSX and Two Micron All Sky Survey (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 H 2 O masers which corresponds to an overall detection rate of ∼50 per cent. We find no significant difference in the detection rate for H II regions and MYSOs which would suggest that the conditions required to produce maser emission are equally likely in both phases. Comparing the detection rates as a function of luminosity, we find the H 2 O detection rate has a positive dependence on the source luminosity, with the detection rate increasing with increasing luminosity.We detect ammonia emission towards 479 of these massive young stars, which corresponds to ∼80 per cent. 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, full width at half-maximum linewidth and total NH 3 column density for the sample are approximately 22 K, 2 km s −1 and 2 × 10 15 cm −2 , respectively. We find that the NH 3 (1,1) linewidth 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 linewidth-clump mass relationship.The velocities of the peak H 2 O masers and the NH 3 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 H 2 O 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 H 2 O maser.

Radio and infrared study of the star-forming region IRAS 20286+4105

“…As shown in the figure, there are a number of masers detected towards IRAS 20286+4105. The positions of H2O & NH3 masers detected by Urquhart et al (2011) are coincident with that of RS1. Water masers are known for their closest association with outflows from young stars (de Buizer et al 2005).…”

“…IRAS 20286+4105 has also been the target of many surveys to detect masers. Water, ammonia and Class I Methanol masers have been detected towards this region (Palla et al 1991;Brand et al 1994; Codella, Felli & Natale 1996; Molinari et al 1996; Urquhart et al 2011;Gan et al 2013). However, the search for Class II methanol and hydroxyl masers yielded negative results (van der Walt, Gaylard & MacLeod 1995; Edris, Fuller & Cohen 2007).…”

The physics of water masers observable with ALMA and SOFIA: model predictions for evolved stars

“…Selective surveys of water masers in high-mass young stellar objects (HMYSOs) (Urquhart et al 2009(Urquhart et al , 2011 typically observe towards sources that satisfy certain infra-red colour criteria based, for example, on the Red MSX Source survey, or 4.5 µm emission detected by the GLIMPSE instrument aboard the Spitzer satellite (Yung et al 2013). Unlike 6.7-GHz methanol masers that are believed to be associated only with the formation of high-mass stars (Xu et al 2008), 22-GHz water masers are also associated with low-mass protostellar objects, and surveys of objects of this type include work by Furuya et al (2001) and Furuya et al (2003) (respective errata in Furuya et al (2007b,a)) that showed that water masers are associated primarily with low-mass protostars of class 0 c 2002 RAS with some in class 1.…”

MAGIC reveals a complex morphology within the unidentified gamma-ray source HESS J1857+026

“…3. Ammonia emission, which traces high density (∼10 4 cm −3 ) gas, was also detected by the Red MSX Source (RMS) survey (Urquhart et al 2011), in which the source, MSX6C G036.4057+00.0230, had a NH 3 (1, 1) velocity of V LSR = 57.77 km s −1 . The authors also detected H 2 O maser emission, which indicates on-going star formation.…”