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[8.11] Signatures of the Youngest Starbursts: Optically-thick Thermal Bremsstrahlung Radio Sources in Henize 2-10

H.A. Kobulnicky (U. Wisconsin), K.E. Johnson (U. Colorado)

Very Large Array (VLA) radio continuum imaging reveals compact (<8 pc) ~1 mJy radio sources in the central 5\arcsec\ starburst region of the blue compact galaxy Henize 2-10. While the global radio continuum spectrum is a power law (S_\nu \propto \nu^\alpha) indicative of nonthermal processes (\alpha~q-0.5), the radio sources have positive (\alpha>0.0) spectral indicies suggesting an optically thick thermal bremsstrahlung origin. We model the luminosities and spectral energy distributions of these radio knots, finding that they are consistent with unusually dense H~II regions having electron densities, 1500~cm^-3e<5000~cm^-3, and sizes 3~pc~6 yr, the possible precursors to globular clusters, may be most easily identified by finding compact radio sources with optically-thick thermal bremsstrahlung spectral signatures.

H.A.K. is grateful for support from a Hubble Postdoctoral Fellowship awarded by NASA through the Space Telescope Science Institute. K.E.J. is supported by NASA through a Graduate Student Researchers Program fellowship.

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