The Spitzer Survey of the Small Magellanic Cloud: S3MC Imaging and Photometry in the Mid- and Far-Infrared Wave Bands

We present the initial results from the Spitzer Survey of the Small Magellanic Cloud (S³MC), which imaged the star-forming body of the SMC in all seven MIPS and IRAC wave bands. We find that the F₈/F₂₄ ratio (an estimate of PAH abundance) has large spatial variations and takes a wide range of values that are unrelated to metallicity but anticorrelated with 24 μm brightness and F₂₄/F₇₀ ratio. This suggests that photodestruction is primarily responsible for the low abundance of PAHs observed in star-forming low-metallicity galaxies. We use the S³MC images to compile a photometric catalog of ~400,000 mid- and far-infrared point sources in the SMC. The sources detected at the longest wavelengths fall into four main categories: (1) bright 5.8 μm sources with very faint optical counterparts and very red mid-infrared colors ([5.8]-[8.0]>1.2), which we identify as YSOs; (2) bright mid-infrared sources with mildly red colors (0.16<~[5.8]-[8.0]<0.6), identified as carbon stars; (3) bright mid-infrared sources with neutral colors and bright optical counterparts, corresponding to oxygen-rich evolved stars; and (4) unreddened early B stars (B3-O9) with a large 24 μm excess. This excess is reminiscent of debris disks and is detected in only a small fraction of these stars (<~5%). The majority of the brightest infrared point sources in the SMC fall into groups 1-3. We use this photometric information to produce a catalog of 282 bright YSOs in the SMC with a very low level of contamination (~7%).