SURVEYING THE AGENTS OF GALAXY EVOLUTION IN THE TIDALLY STRIPPED, LOW METALLICITY SMALL MAGELLANIC CLOUD (SAGE-SMC). I. OVERVIEW

Abstract

The Small Magellanic Cloud (SMC) provides a unique laboratory for the study\nof the lifecycle of dust given its low metallicity (~1/5 solar) and relative\nproximity (~60 kpc). This motivated the SAGE-SMC (Surveying the Agents of\nGalaxy Evolution in the Tidally-Stripped, Low Metallicity Small Magellanic\nCloud) Spitzer Legacy program with the specific goals of studying the amount\nand type of dust in the present interstellar medium, the sources of dust in the\nwinds of evolved stars, and how much dust is consumed in star formation. This\nprogram mapped the full SMC (30 sq. deg.) including the Body, Wing, and Tail in\n7 bands from 3.6 to 160 micron using the IRAC and MIPS instruments on the\nSpitzer Space Telescope. The data were reduced, mosaicked, and the point\nsources measured using customized routines specific for large surveys. We have\nmade the resulting mosaics and point source catalogs available to the\ncommunity. The infrared colors of the SMC are compared to those of other nearby\ngalaxies and the 8 micron/24 micron ratio is somewhat lower and the 70\nmicron/160 micron ratio is somewhat higher than the average. The global\ninfrared spectral energy distribution shows that the SMC has ~3X lower aromatic\nemission/PAH (polycyclic aromatic hydrocarbon) abundances compared to most\nnearby galaxies. Infrared color-magnitude diagrams are given illustrating the\ndistribution of different asymptotic giant branch stars and the locations of\nyoung stellar objects. Finally, the average spectral energy distribution (SED)\nof HII/star formation regions is compared to the equivalent Large Magellanic\nCloud average HII/star formation region SED. These preliminary results are\nexpanded in detail in companion papers.\n