Astrophysical Maser Group: Research Topics

Methanol masers in a candidate circumstellar disk

From Harvey-Smith et al. (2008) published in Monthly Notices of the Royal Astronomical Society

We published the first images of 6.7-GHz methanol masers in the massive star-forming region DR21(OH)N, observed using the Multi Element Radio Linked Interferometer Network (MERLIN). The intrinsic angular resolution of the observations was 43 mas (~100 AU at the distance of DR21), but structures far smaller than this were revealed by employing a centroid mapping technique. This was used in an attempt to identify the physical structure (e.g. disc, outflow, shock) associated with the methanol masers. In DR21(OH)N the methanol masers trace an arc with a double-peaked profile and a complex velocity gradient. This velocity gradient closely resembles that of a Keplerian disc. The masers in the arc are 4.5% linearly polarized, with a polarization angle that indicates that the magnetic field direction is roughly perpendicular to the large-scale magnetic field in the region (indicated by lower angular resolution measurements of the CO and dust polarization).

We have now followed up these observations using the European VLBI Network, which has far superior angular resolution. The paper is in preparation so check this website very soon for the results!

Measuring magnetic fields in distant galaxies

From Robishaw et al. (2008) published in The Astrophysical Journal

Using radio emission from the 1667 MHz rotational transition of extragalactic hydroxyl, we have made the first direct detection of magnetic fields in a galaxy other than our own Milky Way by means of Zeeman splitting. We've found milligauss-strength fields in 4 starburst galaxies including Arp 220 (left - Credit NASA, ESA & C. Wilson).

The radio emission that we detect comes from clouds of gas deep inside these distant star-forming galaxies. These clouds emit extremely bright laser emission at microwave wavelengths and therefore called masers. Because they're so bright, large and surround the entire nucleus of the galaxy they're called megamasers.

Proper motion studies of masers in W3(OH)

We are undertaking a `proper motion' study of methanol 6.7-GHz masers in W3(OH) using VLBI observations separated by 15 years. Measuring the proper motion of the masers (i.e. the movement of the maser emission across the sky with time) allows us to measure the motion of energised molecular gas in the region. In W3(OH), there appears to be a highly collimated feature in the central cluster of masers that is rapidly becoming more linearly extended. We are also testing the measurements of Kawamura and Masson that showed the ultra-compact HII region is expanding at 3-5 km/s. The paper is in preparation, but here is a project webpage written by a year 10 student who undertook some of the work during a week-long project at the School of Physics

Linear polarization of excited OH masers in W3(OH)

We are undertaking a study of the magnetic fields in the massive star-forming region W3(OH) by observing the polarization of hydroxyl masers. Here is a poster on our preliminary results from the IAU Symposium on Astrophysical Masers.