Global very long-baseline interferometry observations of compact radio sources in M82

Observations of the starburst galaxy, M82, have been made with a 20-station global very long-baseline interferometry (VLBI) array at lambda 18 cm. Map s are presented of the brightest young supernova remnants (SNR) in M82 and the wide-field mapping techniques used in making images over a field of vie w of similar to1 arcmin with 3-milliarcsecond resolution are discussed. A l imit has been placed on the power-law deceleration of the young supernova r emnant (SNR) 43.31+592 with an index greater than 0.73 +/-0.11 from observa tions with the European VLBI Network. Using the global array we have resolv ed compact knots of radio emission in the source which, with future global observations, will enable better constraints to be placed on the expansion parameters of this SNR. The latest global observations have also provided high-resolution images of the most compact radio source in M82, 41.95+575. We determine an upper lim it to the radial expansion rate along the major axis of 2000 km s(-1). Howe ver, the new images also show structure resembling that of collimated eject ion which brings into question the previous explanation of the source as be ing a result of the confinement of a supernova by a high-density circumstel lar medium. It is apparent that we are now able to image the brightest supernova remnan ts in M82 with a linear scale which allows direct comparison with galactic SNR such as Cassiopeia A.