The three-dimensional structure of the giant stellar stream in Andromeda

The wide-field CCD camera at the Canada-France-Hawaii Telescope (CFHT) was used to survey the giant stellar stream in the Andromeda galaxy, resolving stars down the red giant branch in M31 to I similar or equal to 25, a magnitude deeper than our previous Isaac Newton Telescope (INT) survey of this galaxy and extending 1degrees further out. The stream is seen to extend out to the south-east of M31 as far as we have surveyed (some , corresponding to a projected distance of similar to60 kpc). It is a linear structure in projection, and the eastern edge of the stream presents a sharp boundary in star counts, suggesting that it remains a coherent structure. By analysing the luminosity function of the metal-rich component of the stream, we find that, at the furthest extent of our survey, the stream is 100 kpc further away along the line of sight than M31. It can then be traced to a point on the north-western side of the galaxy where it is some 30 kpc in front of M31, at which point the stream turns away from our survey area.