A Multibeam Search-Engine for Methanol Masers

The Multibeam Project

A 7-beam receiver system for the Lovell Telescope at Jodrell Bank and the Parkes 64-m radio telescope will come into operation in 2005. This is a joint UK-Australian collaboration, involving 8 UK institutes. The receiver system, which covers the frequency range 6.0-6.7 GHz, is being constructed jointly at Jodrell Bank Observatory and the Australia Telescope National Facility. The system will be powerful enough to detect all the methanol 6.7-GHz masers in the Galaxy, and the brightest methanol masers in the Magellanic Clouds and other Local Group galaxies. The receiver will have other uses as well, including pulsar, recombination line and continuum surveys.

Methanol Masers and Star Formation

Although massive stars constitute only 10% of the mass of a galaxy, they dominate the luminosity, the energy input to the interstellar medium, the supply of heavy elements and, through their powerful UV-radiation, the temperature of the ISM. Cosmic masers are arguably the best tool we have to locate regions of massive star formation in our own Galaxy at a key stage in their evolution, and study them at high angular resolution.

Since its discovery, the methanol 6.7-GHz maser has been recognized as one of the brightest signposts to the formation of massive young stars (Menten 1991). It is the second strongest cosmic maser known (after water at 22 GHz), it is widespread and, unlike all other strong masers it is only found close to massive young stars. A survey for methanol 6.7-GHz masers is therefore a relatively quick and simple way to find these stars in the Galaxy, or in nearby galaxies. The high photon rate of the masers makes them readily detectable and their compact size eliminates problems with blending from extended emission (which is a limitation in the infrared and sub-mm wavebands).

Most methanol masers have been found in targetted searches of known star-forming regions and IRAS sources (Caswell & Vaile et al. 1995; Walsh et al. 1997; Szymczak et al. 2000). Systematic surveys have been limited to latitudes within 0.5 degrees of the galactic plane, with limited longitude coverage, and using 30-m class dishes (Ellingsen et al. 1996). When equipped with a 7-beam receiver, the upgraded Lovell Telescope and the Parkes Telescope will be two orders of magnitude faster, as search instruments, than these smaller dishes. The Milky Way survey is likely to double the number of methanol masers known. The resulting catalogue of masers will provide a major resource for many follow-up investigations at other wavelengths.

The PhD

First light is expected in late 2005, so the time is right for a new PhD student to get involved with the project. The student will be able to take part in commissioning the receiver on the Parkes Telescope and in follow-up work using the Australia Telescope Compact Array (ATCA) to measure accurate positions. The right student could also help with software development for COBRA (which will take the spectra during the Jodrell Bank phase of the survey, in 2007).

Caswell, J. L., Vaile, R. A., Forster, J. R., 1995, MNRAS, 277, 210-216
Ellingsen, S. P., et al., 1996, MNRAS, 280, 378-396.
Menten, K., 1991, ApJ 380, L75-L78.
Szymczak, M., Hyrnek, G., Kus, A. J., 2000, A&AS, 143, 269-301.
Walsh, A. J., Hyland, A. R., et al., 1997, MNRAS, 291, 261-278.