• DOI:10.1038/nature06460
• Corpus ID: 4387133

Two stellar components in the halo of the Milky Way

@article{Carollo2007TwoSC,
  title={Two stellar components in the halo of the Milky Way},
  author={Daniela Carollo and Timothy C. Beers and Young Sun Lee and Masashi Chiba and John E. Norris and Ronald Wilhelm and T. S. Sivarani and Brian Elliott Marsteller and Jeffrey A. Munn and Coryn A. L. Bailer-Jones and Paola Re Fiorentin and Donald G. York},
  journal={Nature},
  year={2007},
  volume={450},
  pages={1020-1025}
}

• D. Carollo, T. Beers, +9 authors D. York
• Published 20 June 2007
• Physics
• Nature

The halo of the Milky Way provides unique elemental abundance and kinematic information on the first objects to form in the Universe, and this information can be used to tightly constrain models of galaxy formation and evolution. Although the halo was once considered a single component, evidence for its dichotomy has slowly emerged in recent years from inspection of small samples of halo objects. Here we show that the halo is indeed clearly divisible into two broadly overlapping structural components—an inner and an outer halo—that exhibit different spatial density profiles, stellar orbits and stellar metallicities (abundances of elements heavier than helium). The inner halo has a modest net prograde rotation, whereas the outer halo exhibits a net retrograde rotation and a peak metallicity one-third that of the inner halo. These properties indicate that the individual halo components probably formed in fundamentally different ways, through successive dissipational (inner) and dissipationless (outer) mergers and tidal disruption of proto-Galactic clumps.