Probing Star Formation at Low Metallicity: the Radio Emission of Super Star Clusters in Sbs0335−052

We present high-resolution radio continuum observations of the nascent starburst in the metalpoor galaxy SBS 0335−052. These radio data were taken with the Very Large Array and include observations at 0.7 cm, 1.3 cm, 2 cm, 3.6 cm, and 6 cm. These observations enable us to probe the thermal radio nebulae associated with the extremely young star-forming regions in this galaxy. Two discrete and luminous star-forming regions are detected in the south of the galaxy that appear to be associated with massive star clusters previously identified at optical wavelengths. However, the remaining optically-identified massive star clusters are not clearly associated with radio emission (either thermal or non-thermal) down to the sensitivity limits of these radio data. The spectral energy distributions of the two radio-detected clusters are consistent with being purely thermal, and the entire region has an inferred ionizing flux of ∼ 1.2 × 10s, which is equivalent to ∼ 12, 000 “typical” Otype stars (type O7.5 V). The observations presented here have resolved out a significant contribution from diffuse non-thermal emission detected previously, implying a previous episode of significant star formation. The current star formation rate (SFR) for this southern region alone is ∼ 1.3 M⊙yr , or ∼ 23 M⊙yr kpc, which is nearing the maximum starburst intensity limit. This SFR derived from thermal radio emission also suggests that previous optical recombination line studies are not detecting a significant fraction of the current star formation in SBS 0335−052. From model fits to the radio spectral energy distribution, we infer a global mean density in the two youngest clusters of ne & 10 3 − 10 cm. In addition, a comparison between the compact and diffuse radio emission indicates that up to ∼ 50% of the ionizing flux could be leaking out of the compact Hii regions; this in is agreement with previous work which suggests that the interstellar medium surrounding the natal clusters in SBS 0335−052 is porous and clumpy. Subject headings: galaxies:individual(SBS 0335-052) – galaxies: star clusters – galaxies: starburst – HII regions – stars: formation