The deeply embedded starburst in SBS 0335-052

We present 4 mum ISAAC imaging and spectroscopy of the extremely metal-poor dwarf galaxy SBS 0335-052, aimed at a better understanding of the dust in this low-metallicity galaxy. The 4 mum emission turns out to be very compac t, confined to the brightest pair of Super Star Clusters (SSCs). The K-S-L' color is extremely red, and the L' emission is consistent with the extrapo lation of the ISO mid-infrared spectral energy distribution (SED). From hyd rogen recombination lines and a fit to the near-/mid-infrared SED, we confi rm a visual extinction of greater than or similar to 15 mag. Our data sugge st that the sites of the optical and infrared emission are distinct: the op tical spectral lines come from an almost dustless region with a high star f ormation rate and a few thousand OB stars. This region lies along the line- of-sight to a very dusty central star cluster in which there are more than three times as many massive stars, completely hidden in the optical. From t he extinction, we derive an upper limit for the dust mass of 10(5) M-circle dot which could be produced by recent supernovae.