M82 - MERLIN & VLA
The nearest starburst, in M82, is being studied intensively with the
VLA, MERLIN and VLBI. The VLA/MERLIN map at 20cm wavelength is the
best overall representation of the radio source. As well as diffuse
emission there are $\sim 50$ compact sources many which have been
resolved into shells. The shell structures confirm that the compact
sources are indeed supernova remnants (SNR) and hence M82 is a
convenient laboratory for studying SNR. European VLBI observations
over an 11 year time baseline have measured expansion velocities of
±9000 km/s in several remnants indicating that their ages
range from about 35 to about 100 years. Assuming similar expansion
velocities for the larger shells, mapped with MERLIN, implies that
their ages are up to 1000 years. Future VLBI observations should
enable the ages of many more remants to be estimated and hence allow
the present supernova rate to be determined.
Wills, Muxlow, Pedlar (Manchester)