出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：The structure of the halo of the Milky Way has recently been shown to be clearly divisible into
two overlapping stellar components, the inner and the outer halo. The first structure dominates
at Galactocentric distances R < 10-15 kpc, exhibits highly eccentric orbits, has a slightly prograde
rotation, and comprises stars with a peak in their metallicity distribution function (MDF)
around [Fe/H] = −1.6. The outer-halo component dominates at R > 15-20 kpc, exhibits a much
more uniform distribution of orbital eccentricities, has a clear (and statistically significant) net
retrograde rotation, and comprises stars with a peak in their MDF a factor of three lower than the
inner halo ([Fe/H] = −2.2). Such properties indicate that one might associate two distinct modes
of formation, and timescales, for the assembly of these two structures. The dataset upon which
these claims are based has recently been increased by 50% with the addition of new stars from
SDSS/SEGUE. We present the first results of a Maximum Likelihood technique that provides estimates
for the structural parameters of the inner- and outer-halo components, including estimates
of the fraction of stars within each population as a function of distance. Such numbers are critical
for refining ongoing and future searches for the most metal-poor stars in the Galaxy
