Deep MERLIN 5GHz Radio Imaging of Supernova Remnants in the M82 Starburst

TL;DR

This paper presents the most sensitive high-resolution 5 GHz radio imaging of M82, detecting over 50 sources including supernova remnants and HII regions, and measures their sizes, fluxes, and expansion velocities over a 9.75-year period.

Contribution

It provides the deepest 5 GHz radio image of M82 to date and measures expansion velocities of supernova remnants, revealing their sizes and dynamics with unprecedented detail.

Findings

Over 50 sources detected, mostly supernova remnants and HII regions.

Supernova remnant diameters range from 0.3 to 6.7 pc.

Expansion velocities range from 2200 to 10500 km/s.

Abstract

The results of an extremely deep, 8-day long observation of the central kpc of the nearby starburst galaxy M82 using MERLIN (Multi-Element Radio Linked Interferometer Network) at 5 GHz are presented. The 17E-06 Jy/beam, rms noise level in the naturally weighted image make it the most sensitive high resolution radio image of M82 made to date. Over 50 discrete sources are detected, the majority of which are supernova remnants, but with 13 identified as HII regions. Sizes, flux densities and radio brightnesses are given for all of the detected sources, which are all well resolved with a majority showing shell or partial shell structures. Those sources within the sample which are supernova remnants have diameters ranging from 0.3 to 6.7 pc, with a mean size of 2.9 pc. From a comparison with previous MERLIN 5 GHz observations made in July 1992, which gives a 9.75 year timeline, it has been possible to measure the expansion velocities of ten of the more compact sources, eight of which have not been measured before. These derived expansion velocities range between 2200 and 10500 km/s.