2004ApJS..154..211H

SBS 0335-052 is a blue compact dwarf galaxy (BCD) with one of the lowest known metallicities, Z∼Z_☉/41, making it a local example of how primordial starburst galaxies and their precursors might appear. A spectrum obtained with the Infrared Spectrograph (IRS) on the Spitzer Space Telescope clearly shows silicate absorption features and emission lines of [S IV] and [Ne III], and puts strong upper limits on the polycyclic aromatic hydrocarbon (PAH) emission features. The observed low-resolution spectrum (R∼90) extends from 5.3 to 35 µm and peaks at ∼28 µm. The spectrum is compared to IRS observations of the prototypical starburst nucleus NGC 7714. SBS 0335-052 is quite unlike normal starburst galaxies, which show strong PAH bands, low-ionization emission lines, and a continuum peak near 80 µm. The continuum difference for λ>30 µm implies a substantial reduction in the mass of cold dust. If the spectrum of this very low-metallicity galaxy is representative of star-forming galaxies at higher redshifts, it may be difficult to distinguish them from active galactic nuclei, which also show relatively featureless flat spectra in the mid-IR.