Optical and Ultraviolet Morphology of the Starburst Regions in Wolf-Rayet Galaxies

Summary

Wolf-Rayet galaxies are a subset of starburst galaxies whose integrated spectra reveal the presence of hundreds to thousands of Wolf-Rayet stars. These galaxies exhibit a number of other properties indicative of a large “starburst” population of young, hot, massive stars. We have obtained optical ground-based and ultraviolet HST images of several Wolf-Rayet galaxies and present examples of the spatial morphologies observed at these wavelengths. Large star-forming regions which appear to be single units in the optical are resolved into numerous compact bright knots in the ultraviolet HST images. These multiple starburst knots are typically less than 100 pc in size and too small and closely spaced to be detected individually in the ground-based optical images. Yet they contain large numbers of hot stars and are typically several times as luminous as 30 Doradus, the giant HII region in the LMC. The intense bursts of star formation in these knots probably began only a few Myr ago and lasted less than about 1 Myr. It is possible that these knots represent proto-globular clusters which were formed as the result of recent galaxy mergers and/or interactions.

Introduction

Wolf-Rayet (W-R) galaxies are a subset of HII galaxies in whose integrated optical spectra a broad resolved HeII λ4686 emission feature has been detected (Conti 1991 and references therein).