Detecting substructure in the galactic stellar halo with Gaia

We present a Gaia mock catalogue we have created to test various approaches to detect the presence of past mergers in the Galactic halo. We propose an extension of the great circle cell method of Johnston et al. (1996), which is optimized to identify tidal debris along great circles in the sky. We have added the proper motion information that will be supplied by Gaia to add a kinematical restriction to the original method. We test our extended method using N-body satellites with realistic star formation histories. We investigate the limits of detectability as a function of satellite luminosity, star formation history and orbit. We find the inclusion of of the kinematical restriction greatly enhances the success rate of the method.