Galactic Halo Stellar Structures in the Triangulum-andromeda Region∗

This letter reports on the Galactic stellar structures that appear in the foreground of our CanadaFrance-Hawaii-Telecopse/MegaCam survey of the halo of the Andromeda galaxy. We recover the main sequence and main sequence turn-off of the Triangulum-Andromeda structure recently found by Majewski and collaborators at a heliocentric distance of ∼ 20 kpc. The survey also reveals another less populated main sequence at fainter magnitudes that could correspond to a more distant stellar structure at ∼ 28 kpc. Both structures are smoothly distributed over the ∼ 76deg covered by the survey although the closer one shows an increase in density by a factor of ∼ 2 towards the North-West. The discovery of a stellar structure behind the Triangulum-Andromeda structure that itself appears behind the low-latitude stream that surrounds the Galactic disk gives further evidence that the inner halo of the Milky Way is of a spatially clumpy nature. Subject headings: Galaxy: evolution — Galaxy: halo — Galaxy: structure — Local Group