| Young, massive stars profoundly affect the interstellar medium (ISM) in galaxies. Many of these effects are traceable in the radio continuum. The dwarf galaxy M82 is undergoing a burst of star formation so intense that its emission properties across the spectrum are dominated by the effects of new stars.; A 5-band radio continuum study of the nucleus of M82 is presented. A method is discussed whereby the data are imaged with the best possible noise characteristics.; A total of 73 compact sources are catalogued. Their radio emission has been modeled using the combined effects of non-thermal and thermal emission and thermal absorption. Full spectral models are fit to 26 sources, identifying them as either supernova remnants (SNR's) or compact HII regions.; The wispy, diffuse interstellar radio emission has been imaged at about 1''.0 resolution (17.6 pc) over five frequencies, and spectrally decomposed into images of thermal-only and non-thermal-only emission. The thermal emission is clearly organized into three regions: a central ring around the stellar nucleus, and two ionized lanes extending eastward and westward along the major axis. These regions are further organized into clumps. Each clump is comparable in size and energy output to the largest, locally known extragalactic H II regions.; The derived supernova rates are used in conjunction with other observations to constrain starburst models. The models cannot reproduce the properties of M82 using a solar neighbourhood stellar initial mass function (IMF). IMF's that are biased against the formation of low mass stars are required.; The integrated radio emission of the galaxy predicts a higher supernova rate than that predicted using either the "ring source" or the continuity equation method. Since the integrated radio emission records an historical rate from sources that have already been dispersed into the ISM, the implication is that the supernova rate is decreasing over time and therefore the starburst in M82 in coming to an end. This prediction is in agreement with other evidence from a consideration of star formation rates and the amount of available molecular material. (Abstract shortened by UMI.)... |
