1DSM/DAPNIA/SAp, CEA-Saclay, 91191 Gif sur Yvette Cedex FRANCE
2 Astronomy Dept., University of Virginia, PO Box 3818, University station, Charlottesville, VA 22903-8181, USA
The extremely metal-deficient (
)
blue compact dwarf galaxy
SBS 0335-052 was observed with ISOCAM using a combination of broad
bands and CVF covering the range 5-17.4 microns. With an
of
2.15, the galaxy is unexpectedly bright in the mid-infrared range for
such a low metallicity object.
The mid-infrared spectrum shows none of the classical unidentified infrared bands (e.g. at 11.3 and 12.7 microns), which we interpret either as a sign of destruction of these grains by the rather intense radiation field, or, more, likely, by the absence of that component of dust in the interstellar medium of the galaxy due to its very early stage of chemical evolution.
The spectal energy distribution is in fact dominated by a very strong continuum over which the ionic lines of [SIV] and [NeIII], usually dominant in starburst galaxies, are barely detected. We have tried numerous fits of this continuum, and find that is can be very well represented by a modified black-body emission going through a thick screen of dust. The absorption law that is required for this fits is that derived toward the Galactic center. Our modelling of the observations require an Av of 18-20, which is exceptionnally high for such a ``young'' object. Given the MIR luminosity of SBS 0335-052 this extinction implies that much of the star-formation activity of the galaxy is hidden from the UV-visible domain, a fact that bears significant implications on studies of primeval galaxies.