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SkyMapper Protected Science Project

Mapping the Structure of the Outer Parts of the Magellanic Clouds

Gary Da Costa (RSAA), Ken Freeman (RSAA), Stefan Keller (RSAA), Dougal Mackey (RSAA)

The Small and Large Magellanic Clouds are our nearest significant galaxy neighbours. But have they always been our neighbours? What are their true extents on the sky? And how strongly have gravitational interactions between the Clouds and the Milky Way, and between the Clouds themselves, influenced their evolution? These are important questions and remarkably, they lack clear answers. We intend to use SkyMapper imaging of the full area of the periphery of the Magellanic Clouds to construct detailed 2-dimensional maps of the stellar distribution. With these data we will study the underlying density profile in the extreme outer parts of these galaxies. We shall also investigate the extent and location of any deviations from the underlying profile, seeking particularly possible sub-structures. Such features may be signatures of gravitational interactions, and their orientation and location will indicate whether the primary interaction is between the Clouds themselves or with the Galaxy. Our results will complement and extend those of the ESO VISTA near-IR (Y, J and Ks bands) survey of the Magellanic Clouds (VMC) as the area covered by the SkyMapper imaging is much more extensive - the VMC survey reaches only to ~7deg from the LMC centre. In our analysis of the SkyMapper data we will use matched-filter techniques in which only those stars that fall in particular regions of the multi-dimensional colour-magnitude space dominated by LMC (SMC) members are used in the analysis. In this way we can achieve much improved signal-to-noise over stellar densities derived from single band data. We will also investigate the stellar populations of the extreme outskirts - an old metal-poor halo population should be readily distinguished in the SkyMapper survey photometric bands from an extension of the younger (age ~ few Gyr) more metal-rich population that dominates the inner regions of both Clouds (and from foreground dwarf stars). We will also study the stellar populations in the region between the Clouds where the Magellanic Stream appears to originate. The program requires Main Survey data.