Context. The Red MSX Source (RMS) survey is a multi-wavelength programme of follow-up observations designed to distinguish between genuine massive young stellar objects (MYSOs) and other embedded or dusty objects, such as ultra compact (UC) HII regions, evolved stars and planetary nebulae (PNe). We have identified nearly 2000 MYSOs candidates by comparing the colours of MSX and 2MASS point sources to those of known MYSOs. Aims. There are several other types of embedded or dust enshrouded objects that have similar colours as MYSOs and contaminate our sample. Two sources of contamination are from UCHII regions and PNe, both of which can be identified from the radio emission emitted by their ionised nebulae. Methods. In order to identify UCHII regions and PNe that contaminate our sample we have conducted high resolution radio continuum observations at 3.6 and 6 cm of all southern MYSOs candidates (235• ) using the Australia Telescope Compact Array (ATCA). These observations have a spatial resolution of ∼1-2 and typical image rms noise values of ∼0.3 mJy -sensitive enough to detect a HII region powered by B0.5 star at the far side of the Galaxy. Results. Of the 826 RMS sources observed we found 199 to be associated with radio emission, ∼25% of the sample. The Galactic distribution, morphologies and spectral indices of the radio sources associated with the RMS sources are consistent with these sources being UCHII regions. Importantly, the 627 RMS sources for which no radio emission was detected are still potential MYSOs. In addition to the 802 RMS fields observed we present observations of a further 190 fields. These observations were made towards MSX sources that passed cuts in earlier versions of the survey, but were later excluded.

Context. The Red MSX Source (RMS) survey is an ongoing multi-wavelength observational programme designed to return a large, well-selected sample of massive young stellar objects (MYSOs). We have identified ∼2000 MYSO candidates located throughout the Galaxy by comparing the colours of MSX and 2MASS point sources to those of known MYSOs. The aim of these follow-up observations is to identify other objects with similar colours such as ultra compact (UC) HII regions, evolved stars and planetary nebulae (PNe) and distinguish between genuine MYSOs and nearby low-mass YSOs. Aims. To identify the populations of UCHII regions and PNe within the sample and examine their Galactic distribution. Methods. We have conducted high resolution radio continuum observations at 6 cm towards 659 MYSO candidates in the northern hemisphere (10 • < l < 250 • ) using the Very Large Array (VLA). These observations have a spatial resolution of ∼1-2 and typical image rms noise values of ∼0.22 mJy -sensitive enough to detect a HII region powered by B0.5 star at the far side of the Galaxy. In addition to these targeted observations we present archival data towards a further 315 RMS sources extracted from a previous VLA survey of the inner Galaxy.Results. We present the results of radio continuum observations made towards 974 MYSO candidates, 272 (∼27% of the observed sample) of which are found to be associated with radio emission above a 4σ detection limit (∼1 mJy). Using results from other parts of our multi-wavelength survey we separate these RMS-radio associations into two distinct types of objects, classifying 51 as PNe and a further 208 as either compact or UC HII regions. Including all HII regions and PNe identified either from the literature or from the multi-wavelength data these numbers increase to 391 and 79, respectively. Using this well selected sample of HII regions we estimate their Galactic scale height to be 0.6 • . In addition to the RMS-radio associations we are able to set upper limits on the radio emission of ≤1 mJy for the 702 non-detections, which is below the level expected if they had already begun to ionise their surroundings. Conclusions. Using radio continuum and archival data we have identified 79 PNe and 391 HII regions within the northern RMS catalogue. We estimate the total fraction of contamination by PNe in the RMS sample is of order 10%. The sample of HII regions is probably the best representation to date of the Galactic population of HII regions as a whole.

Context. The Red MSX Source (RMS) survey is an ongoing multi-wavelength observational programme designed to return a large, well-selected sample of massive young stellar objects (MYSOs). We have identified ∼2000 MYSOs candidates located within our Galaxy by comparing the colours of MSX and 2MASS point sources to those of known MYSOs. The aim of our follow-up observations is to identify other contaminating objects such as ultra compact (UC) HII regions, evolved stars and planetary nebulae (PNe) and distinguish between genuine MYSOs and nearby low-mass YSOs. Aims. A critical part of our follow-up programme is to conduct 13 CO molecular line observations in order to determine kinematic distances to all of our MYSO candidates. These distances will be used in combination with far-IR and (sub)millimetre fluxes to determine bolometric luminosities which will allow us to identify and remove nearby low-mass YSOs. In addition these molecular line observations will help in identifying evolved stars which are weak CO emitters. Methods. We have used the 22 m Mopra telescope, the 15 m JCMT and the 20 m Onsala telescope to conduct molecular line observations towards 854 MYSOs candidates located in the 3rd and 4th quadrants. These observations have been made at the J = 1-0 (Mopra and Onsala) and J = 2-1 (JCMT) rotational transition frequency of 13 CO molecules and have a spatial resolution of ∼20 −40 , a sensitivity of T * A 0.1 K and a velocity resolution of ∼0.2 km s −1 . Results. We detect 13 CO emission towards a total of 752 of the 854 RMS sources observed (∼88%). In total 2132 emission components are detected above 3σ level (typically T * A ≥ 0.3 K). Multiple emission profiles are observed towards the majority of these sources -461 sources (∼60%) -with an average of ∼4 molecular clouds detected along the line of sight. These multiple emission features make it difficult to assign a kinematic velocity to many of our sample. We have used archival CS (J = 2-1) and maser velocities to resolve the component multiplicity towards 82 sources and have derived a criterion which is used to identify the most likely component for a further 218 multiple component sources. Combined with the single component detections we have obtained unambiguous kinematic velocities towards 591 sources (∼80% of the detections). The 161 sources for which we have not been able to determine the kinematic velocity will require additional line data. Using the rotation curve of Brand & Blitz (1993) and their radial velocities we calculate kinematic distances for all components detected.

Context. The Red MSX Source (RMS) survey is an ongoing multi-wavelength observational programme designed to return a large, high-resolution mid-infrared colour-selected sample of massive young stellar objects (MYSOs). We have identified ∼2000 MYSO candidates located within our Galaxy by comparing the colours of MSX and 2MASS point sources to those of known MYSOs. The aim of our follow-up observations is to identify other objects with similar colours such as ultra compact (UC) HII regions, evolved stars and planetary nebulae (PNe) and distinguish between genuine MYSOs and nearby low-mass YSOs. Aims. A critical part of our follow-up programme is to conduct 13 CO molecular line observations in order to determine kinematic distances to all of our MYSO candidates. These distances will be used in combination with far-IR and (sub)millimetre fluxes to determine bolometric luminosities which will allow us to identify and remove nearby low-mass YSOs. In addition these molecular line observations will help in identifying evolved stars which are weak CO emitters. Methods. We have used the 15 m James Clerk Maxwell Telescope (JCMT), the 13.7 m telescope of the Purple Mountain Observatory (PMO), the 20 m Onsala telescope and the 22 m Mopra telescope to conduct molecular line observations towards 508 MYSOs candidates located in the 1st and 2nd Quadrants. These observations have been made at the J = 1−0 (Mopra, Onsala and PMO) and J = 2−1 (JCMT) rotational transition frequency of 13 CO molecules and have a spatial resolution of ∼20 −55 , a sensitivity of T * A 0.1 K and a velocity resolution of ∼0.2 km s −1 . We complement these targeted observations with 13 CO spectra extracted from the Galactic Ring Survey (GRS), which have a velocity resolution of ∼0.21 km s −1 and sensitivity T * A 0.13−0.2 K, towards a further 403 RMS sources. Results. In this paper we present the results and analysis of the 13 CO spectra obtained towards 911 MYSO candidates. We detect 13 CO emission towards 780 RMS sources which corresponds to approximately 84% of those observed. A total of 2595 emission components are detected above 3σ level (typically T * A ≥ 0.3 K), with multiple components being observed towards the majority of these sources -520 sources (∼56%) -with an average of ∼4 molecular clouds detected along each line of sight. These multiple emission features make it difficult to assign a unique kinematic velocity to many of our sample. We have used archival CS (J = 2−1) and maser velocities to resolve the component multiplicity towards 175 sources (∼20%) and have derived a criterion which is used to identify the most likely component for a further 191 multiple component sources. Combined with the single component detections we have obtained unambiguous kinematic velocities for 638 of the 780 MYSOs candidates towards which CO is detected (∼80% of the detections). The 141 sources for which we have not been able to determine the kinematic velocity will require additional line data. Using the rotation curve of Brand and Blitz (1993) and th...

We investigate the use of H I data to resolve the near/far ambiguity in kinematic distances of massive young stellar object (MYSO) candidates. Kinematic distances were obtained from 13 CO 1-0 (and N 2 H + ) spectral-line observations with the Mopra Telescope towards 94 candidates selected from the Red MSX Source (RMS) survey in the fourth Galactic quadrant (282 • < l < 350 • ). H I data from the Southern Galactic Plane Survey (SGPS) were used in conjunction with the H I self-absorption (SA) technique to determine the near or far distance. We resolved the kinematic distance ambiguity to 70 per cent of the sources. We can also simultaneously solve for any multiple line-of-sight component sources. We discuss the advantages and disadvantages of this technique in comparison with other methods, and also perform confidence checks on the reliability of using the H I SA technique.We examined the projected location of these sources in both the Galactic plane and longitudevelocity (l-v) diagrams to ascertain any recognizable spiral arm pattern. Although no obvious spiral pattern was found when compared to that proposed by Cordes and Lazio, far distance sources tended to lie on or near spiral arm loci. Near distance sources, however, had peculiar velocity uncertainties consistent with the separation between the spiral arms themselves. The l-v plot shows a more consistent picture, with tangent points of the spiral arm loci easily seen.We conclude that using the H I SA technique to determine kinematic distance ambiguities is a quick and reliable method in most cases, with an 80 per cent success rate in determining the correct designation of whether an object is at the near or far distance.