2008ApJ...682L..33F

The stellar halo of M31 exhibits a startling level of inhomogeneity, in which the ``giant southern stream'' stands out most prominently. Our previous analysis indicates that this stream, as well as several other observed features, are products of the tidal disruption of a single satellite galaxy with stellar mass ∼10<sup>9</sup> M<sub>☉</sub> less than 1 Gyr ago. Here we show that observed features of the stream and halo debris favor a cold, rotating, disklike progenitor over a dynamically hot, nonrotating one. These features include the asymmetric distribution of stars along the stream cross section and its metal-rich core/metal-poor sheath structure. We find that a disklike progenitor can also give rise to arclike features on the minor axis that resemble the recently discovered minor-axis ``streams'', even reproducing their lower metallicity. Although interpreted initially as new, independent tidal streams, our analysis suggests that these minor-axis streams may arise from the progenitor of the giant stream. Overall, our study points the way to a more complete reconstruction of the stream progenitor and its merger with M31, based on the emerging picture that most of the major inhomogeneities observed in the M31 halo share a common origin with the giant stream.