Abstract
(abridged) We present a spectroscopic analysis of five stellar streams (`A', `B', `Cr', `Cp' and `D') as well as the extended star cluster, EC4, which lies within streamC, all discovered in the halo of M31 from our CFHT/MegaCam survey. These spectroscopic results were initially serendipitous, making use of our existing observations from the DEep Imaging Multi-Object Spectrograph mounted on the Keck II telescope, and thereby emphasizing the ubiquity of tidal streams that account for ~70% of the M31 halo stars in the targeted fields. Subsequent spectroscopy was then procured in streamCr/p and streamD to trace the velocity gradient along the streams. For the cluster EC4, candidate member stars with average [Fe/H]~-1.4 (Fe/H_spec=-1.6), are found at v_{hel}=-285 km/s suggesting it could be related to streamCp. No similarly obvious cold kinematic candidate is found for streamD, although candidates are proposed in both of two spectroscopic pointings along the stream (both at -400 km/s). Spectroscopy near the edge of streamB suggests a likely kinematic detection, while a candidate kinematic detection of streamA is found (plausibly associated to M33 rather than M31). The low dispersion of the streams in kinematics, physical thickness, and metallicity makes it hard to reconcile with a scenario whereby these stream structures as an ensemble are related to the giant southern stream. We conclude that the M31 stellar halo is largely made up of multiple kinematically cold streams.
Highlights
Stellar streams represent the visible debris of small galaxies being cannibalized by large galaxies, memorials to the merging process by which the haloes of galaxies are built up
If EC4 is dark matter dominated, we have detected the very first sub-subhalo, possibly explaining its small size
(i) We have uncovered a kinematic substructure at vhel = −349.5 ± 1.8 km s−1 from a spectroscopic field lying in the Ibata et al (2007) Stream ‘C’
Summary
Stellar streams represent the visible debris of small galaxies being cannibalized by large galaxies, memorials to the merging process by which the haloes of galaxies are built up. Of the eight stellar streams that have been identified in the halo of M31, only one has plausibly been identified to a dwarf satellite: the loop connecting to NGC 205 (McConnachie et al 2005). This suggests that the other streams could represent an additional seven ‘uncatalogued’ satellites, some of the streams might be produced by a common progenitor, as suggested by models of Fardal et al (2007, 2008) for the M31 Giant Southern Stream, or in a similar fashion to the Sgr dwarf and its numerous wraps around the MW. It is important to characterize their orbits, metallicities and masses, to understand what their progenitors must have been
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
