Infrared Properties of Low-Metallicity Galaxies

C. W. Engelbracht, K. D. Gordon, K. Misselt, J. D. T. Smith, P. G. Pérez-González, G. H. Rieke, M. W. Werner, L. Vanzi, & B. R. Brandl 2006, in "The Spitzer Space Telescope: New Views of the Cosmos," (ASP Conf. Ser.), eds. L. Armus & W.T. Reach, 357, 215

We present new Spitzer photometry of three low-metallicity galaxies. These galaxies have metallicities more than 30 times lower than the solar value and include the two galaxies with the lowest known metallicities, I Zw 18 and SBS 0335-52. Our IRAC and MIPS data represent the first mid- to far-infrared detections for most of these galaxies and allow us for the first time to explore the range of infrared properties of extremely low metallicity galaxies as a class. We derive dust temperatures, dust masses, and optical/infrared luminosities of the galaxies. To put our sample of low-metallicity galaxies into context, we use infrared colors and spectra of galaxies over the full range of metallicities observed in local galaxies to show that there is a transition metallicity below which PAHs are not observed in galaxies.

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