The RMS Survey: 6 cm continuum VLA observations towards candidate massive YSOs in the northern hemisphere

TL;DR

This study uses 6 cm VLA radio observations to identify and classify massive young stellar objects, HII regions, and planetary nebulae within the RMS survey, providing insights into their Galactic distribution and population statistics.

Contribution

It presents the largest high-resolution radio survey of RMS candidates, classifies radio sources into PNe and HII regions, and estimates their Galactic scale height and contamination levels.

Findings

Radio emission detected in 27% of observed candidates.

Identified 79 PNe and 391 HII regions in the sample.

Estimated Galactic scale height of HII regions as 0.6 degrees.

Abstract

(Abridged) 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 $\sim$2000 MYSO candidates located throughout the Galaxy by comparing the colours of MSX and 2MASS point sources to those of known MYSOs. Aims: To identify the populations of UCHII regions and PNe within the sample and examine their Galactic distribution. Method: We have conducted high resolution radio continuum observations at 6 cm towards 659 MYSO candidates in the northern hemisphere ($10\degr< l < 250\degr$) using the VLA. 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 find radio emission towards 272 ($\sim$27% of the observed sample). 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. Using this well selected sample of HII regions we estimate their Galactic scale height to be 0.6\degr. 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.