Survey of MAgellanic Stellar History - SMASH!

Over the last several years, various discoveries have drastically altered our view of the iconic Magellanic Clouds (MCs), the nearest interacting galaxy system. The best evidence is now that they are on first infall into the Milky Way, that their stellar populations extend much further than previously thought, and that they suffered a close collision that tore out both the well-known Magellanic Stream and a large amount of still undetected stellar debris. Here we propose a community DECam survey of the Clouds mapping 480 deg² (distributed over ∼2400 deg² at ∼20% filling factor) to 24th mag in griz (and u 23 mag) that will supplement the 5000 deg² Dark Energy Surveys partial coverage of the Magellanic periphery, allowing us to map the expected stellar debris and extended populations with unprecedented fidelity. We have already conducted a pilot project demonstrating that DECam will allow us to carry out the following: (1) Map the stellar periphery of the MCs with old main sequence turnoff stars to a surface brightness limit of ∼35 mag/arcsec², revealing relics of their formation and past interactions. (2) Identify the stellar component of the Magellanic Stream and Leading Arm for the first time, if they exist, making them the only Galactic halo tracers with both gaseous and stellar components. (3) Derive spatially-resolved star formation histories covering all ages out to large radii of the MCs that will further complement our understanding of their formation. The combination of this survey and the DES data will allow us to uncover a multitude of stellar structure that will unveil the complex and dramatic history of these two dwarf galaxies, while enabling a broad spectrum of community-led projects.

SMASH has obtained initial data through DECam Science Verification (data public now) and through first observing runs in 2013A. Subsequent observations to fulfill the science goals described below have been proposed through the NOAO Survey program.