The Red MSX Source Survey


The Red MSX Source (RMS) survey was conceived at Leeds to systematically search the entire Galaxy for massive young stellar objects (MYSOs). MYSOs are luminous (L > 104 Lsun), embedded infrared sources that have yet to begin ionising their surroundings to form an ultra-compact H II region. They are likely to be already burning hydrogen in their cores, whilst still accreting at the surface. They drive bipolar molecular outflows and often have a compact ionised stellar wind and associated maser activity. Most of their energy comes out in the infrared after reprocessing by the dense circumstellar dust envelope. This is therefore the most logical and unbiased way of searching for such objects. Ideally we would use the far-IR where the spectral energy distribution peaks. The only existing survey at these wavelengths is that by the IRAS satellite, but that suffers from confusion in the galactic plane. Hence, previous searches for MYSOs using IRAS data have been biased towards bright, isolated examples (e.g. Molinari et al. 1998; Sridharan et al. 2002). The much higher resolution mid-IR survey of the galactic plane by the MSX satellite (Price et al. 2001) provided the opportunity for a large comprehensive search for MYSOs in the galaxy. Of course the use of mid-IR selection means that we will not detect earlier phases like the hot molecular cores.

We select sources from the MSX point source catalogue that have the same colours as well-known MYSOs. In addition, we use near-IR data from the 2MASS survey. We do not demand a detection as that would rule out many of the very embedded or obscured MYSOs that we want to detect, but use it to eliminate objects too blue in the near-IR to be MYSOs. The colour selection process (Lumsden et al. 2002) yielded about 2000 candidate MYSOs after further visual inspection of the MSX images had eliminated a significant number of sources that did not appear to be point-like despite being listed in the MSX PSC. Colour-colour diagrams with the colour cuts indicated are shown below.


Many other objects have very similar near- and mid-IR colours to the very red MYSOs we are looking for. These include ultra-compact H II regions, compact planetary nebulae, low-mass YSOs and evolved stars. Hence, we are carrying out an extensive multi-wavelength campaign to identify and eliminate these confusing objects from the sample.  It is this follow-up work that enables the RMS survey to deliver the large sample of MYSOs that will open up a new era of systematic and statistical studies of this important phase of massive star formation.

The RMS Database

The RMS survey database can be found here.