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We examine the nature, possible orbits and physical properties of theprogenitor of the North-western stellar stream (NWS) in the halo of theAndromeda galaxy (M31). The progenitor is assumed to be an accreting dwarfgalaxy with globular clusters (GCs). It is, in general, difficult to determinethe progenitor's orbit precisely because of many necessary parameters.Recently, Veljanoski et al. 2014 reported five GCs whose positions and radialvelocities suggest an association with the stream. We use this data toconstrain the orbital motions of the progenitor using test-particlesimulations. Our simulations split the orbit solutions into two branchesaccording to whether the stream ends up in the foreground or in the backgroundof M31. Upcoming observations that will determine the distance to the NWS willbe able to reject one of the two branches. In either case, the solutionsrequire that the pericentric radius of any possible orbit be over 2 kpc. Weestimate the efficiency of the tidal disruption and confirm the consistencywith the assumption for the progenitor being a dwarf galaxy. The progenitorrequires the mass $\ga 2\times10^6 M_{\sun}$ and half-light radius $\ga 30$ pc.In addition, $N$-body simulations successfully reproduce the basic observedfeatures of the NWS and the GCs' line-of-sight velocities.

The nature of the progenitor of the M31 North-western stream: globular clusters as milestones of its orbit