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J.S. Ulvestad (NRAO), K.E. Johnson (UVa), S.G. Neff (NASA's GSFC)
We have used the VLBI High Sensitivity Array (VLBA with VLA, Green Bank Telescope, and Arecibo) to search for young radio supernovae in three nearby dwarf galaxies containing Super Star Clusters (SSCs) and signs of extreme star formation in the last few million years. No milliarcsecond radio sources were detected in II Zw 40, He 2-10, or NGC 5253, implying that these galaxies contain few radio supernovae, despite the fact that they have at least some star formation going back to 10 million years ago. The upper limits of the source powers range from ~3\times 1017 W/Hz to ~ 1\times 1018 W/Hz at 5 GHz, roughly 0.5 to 1.5 times the power of the galactic supernova remnant Cassiopeia A. Comparison with the radio supernova population in Arp 299 implies that the current supernova rates in the three dwarf galaxies are well below 0.1/yr, and perhaps below 0.01/yr. This result indicates that the SSCs in all three target galaxies probably have formed the majority of their massive stars in the last 3 million years.
The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.