Volume 474, Number 3, November II 2007
|Page(s)||891 - 901|
|Section||Interstellar and circumstellar matter|
|Published online||23 October 2007|
The RMS survey
13CO observations of candidate massive YSOs in the southern Galactic plane
School of Physics and Astrophysics, University of Leeds, Leeds LS2 9JT, UK e-mail: firstname.lastname@example.org
2 Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead CH41 1LD, UK
3 Department of Physics and Astronomy, University of British Columbia, 6224 Aricultural Road, Vancouver, BC, V6T 1Z1, Canada
4 School of Physics and Astronomy, University of New South Wales, Sydney, NSW 2052, Australia
5 Jodrell Bank Observatory, University of Manchester, Cheshire SK11 9DL, UK
6 École Normale Supérieure, Département de Physique, 24 rue Lhomond, 75005 Paris, France
Accepted: 18 August 2007
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 13CO 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 13CO molecules and have a spatial resolution of ~20´´-40´´, a sensitivity of 0.1 K and a velocity resolution of ~0.2 km s-1.
Results.We detect 13CO emission towards a total of 752 of the 854 RMS sources observed (~88%). In total 2132 emission components are detected above 3σ level (typically 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.
Key words: stars: formation / stars: early-type / stars: pre-main sequence / ISM: clouds / ISM: kinematics and dynamics
© ESO, 2007
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