The Extraordinary Mid‐infrared Spectrum of the Blue Compact Dwarf Galaxy SBS 0335−052

SBS0335-052 is a blue compact dwarf galaxy (BCD) with one of the lowest knownmetallicities, Z$\sim$Z$_{\sun}$/41, making it a local example of howprimordial starburst galaxies and their precursors might appear. A spectrumobtained with the Infrared Spectrograph (IRS) on the Spitzer Space Telescopeclearly shows silicate absorption features, emission lines of [SIV] and[NeIII], and puts strong upper limits on the PAH emission features. Theobserved low resolution spectrum (R~90) extends from 5.3 to 35microns and peaksat ~28microns. The spectrum is compared to IRS observations of the prototypicalstarburst nucleus NGC7714. SBS0335-052 is quite unlike normal starburstgalaxies, which show strong PAH bands, low ionization emission lines, and acontinuum peak near 80microns. The continuum difference for $\lambda >30 \mu$mimplies a substantial reduction in the mass of cold dust. If the spectrum ofthis very low metallicity galaxy is representative of star forming galaxies athigher redshifts, it may be difficult to distinguish them from AGNs which alsoshow relatively featureless flat spectra in the mid-IR.Comment: Accepted in ApJ Sup. Spitzer Special Issue, 4 pages, 2 figure