The RMS survey - 6 cm continuum VLA observations towards candidate massive YSOs in the northern hemisphere

By J. Urquhart, M. Hoare, C. Purcell, S. Lumsden, R. D. Oudmaijer, T. Moore, A. Busfield, J. Mottram, B. Davies. 2009

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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.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/de6812f6487a727e03f73caf2b9fd9fb4a18c499

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Citations in the corpus

• The RMS Survey: Ammonia and water maser analysis of massive star forming regions. ⋆ (2011, methodology): “We have obtained arcsecond-resolution radio continuum with ATCA and the VLA (Urquhart et al. 2007, 2009) to identify UC Hii regions and PNe, whilst observations of13CO transitions (Urquhart et al. 2007, 2008) deliver kinematicdistances and luminosities, which allow us to distinguish between nearby…”
• THE GREEN BANK TELESCOPE H ii REGION DISCOVERY SURVEY. II. THE SOURCE CATALOG (2011, background): “Four of these sources were detected as part of the RMS survey (Urquhart et al. 2009) and these authors classify them as PNe.”
• ATLASGAL — towards a complete sample of massive star forming clumps ⋆ (2014, background): “These included radio continuum observations (Urquhart et al. 2007b, 2009), a mixture of targeted mid-infrared imaging (e.g. Mottram et al. 2007) and archival images obtained by the Spitzer GLIMPSE legacy project MNRAS 443, 1555–1586 (2014) D ow nloaded from https://academ ic.oup.com /m…”
• THE WISE CATALOG OF GALACTIC H ii REGIONS (2013, background): “For Urquhart et al. (2007a, 2009) and Sanchez-Monge et al. (2013), we search within radii of 30′′ and 3 The Astrophysical Journal Supplement Series, 212:1 (18pp), 2014 May Anderson et al. (A color version of this figure is available in the online journal.) find 45, 10, and 28 matches, respectively.”
• THE RED MSX SOURCE SURVEY: THE MASSIVE YOUNG STELLAR POPULATION OF OUR GALAXY (2013, background): “…kinematic distances (Urquhart et al 2007a, 2008); radio images to study the HII region and planetary nebulae populations (either our own imaging data – Urquhart et al 2007b, 2009 – or the images present in the CORNISH radio survey – Hoare et al. 2012, Purcell et al. 2013); and finally, for those…”