Substructure around M31: Evolution and Effects

We investigate the evolution of a population of 100 dark matter satellitesorbiting in the gravitational potential of a realistic model of M31. We findthat after 10 Gyr, seven subhalos are completely disrupted by the tidal fieldof the host galaxy. The remaining satellites suffer heavy mass loss andoverall, 75% of the mass initially in the subhalo system is tidally stripped.Not surprisingly, satellites with pericentric radius less than 30 kpc sufferthe greatest stripping and leave a complex structure of tails and streams ofdebris around the host galaxy. Assuming that the most bound particles in eachsubhalo are kinematic tracers of stars, we find that the halo stellarpopulation resulting from the tidal debris follows an r^{-3.5} density profileat large radii. We construct B-band photometric maps of stars coming fromdisrupted satellites and find conspicuous features similar both in morphologyand brightness to the observed Giant Stream around Andromeda. An assumed starformation efficiency of 5-10% in the simulated satellite galaxies results ingood agreement with the number of M31 satellites, the V-band surface brightnessdistribution, and the brightness of the Giant Stream. During the first 5 Gyr,the bombardment of the satellites heats and thickens the disk by a smallamount. At about 5 Gyr, satellite interations induce the formation of a strongbar which, in turn, leads to a significant increase in the velocity dispersionof the disk.Comment: 45 pages, 18 figures. To be submitted to the Astrophysical Journal, version 2.0 : scale height value corrected, references added, and some figures have been modifie