3 research outputs found
Linking dwarf galaxies to halo building blocks with the most metal-poor star in Sculptor
Current cosmological models indicate that the Milky Way's stellar halo was
assembled from many smaller systems. Based on the apparent absence of the most
metal-poor stars in present-day dwarf galaxies, recent studies claimed that the
true Galactic building blocks must have been vastly different from the
surviving dwarfs. The discovery of an extremely iron-poor star (S1020549) in
the Sculptor dwarf galaxy based on a medium-resolution spectrum cast some doubt
on this conclusion. However, verification of the iron-deficiency and
measurements of additional elements, such as the alpha-element Mg, are
mandatory for demonstrating that the same type of stars produced the metals
found in dwarf galaxies and the Galactic halo. Only then can dwarf galaxy stars
be conclusively linked to early stellar halo assembly. Here we report
high-resolution spectroscopic abundances for 11 elements in S1020549,
confirming the iron abundance of less than 1/4000th that of the Sun, and
showing that the overall abundance pattern mirrors that seen in low-metallicity
halo stars, including the alpha-elements. Such chemical similarity indicates
that the systems destroyed to form the halo billions of years ago were not
fundamentally different from the progenitors of present-day dwarfs, and
suggests that the early chemical enrichment of all galaxies may be nearly
identical.Comment: 16 pages, including 2 figures. Accepted for publication in Nature. It
is embargoed for discussion in the press until formal publication in Natur
Stellar archeology: a cosmological view of dwarf galaxies
The origin of dwarf spheroidal galaxies (dSphs) is investigated in a global
cosmological context by simultaneously following the evolution of the Milky Way
Galaxy and its dwarf satellites. This approach enable to study the formation of
dSphs in their proper birth environment and to reconstruct their own merging
histories. The proposed picture simultaneously accounts for several dSph and
Milky Way properties, including the Metallicity Distribution Functions of
metal-poor stars. The observed features are interpreted in terms of physical
processes acting at high redshifts.Comment: 8 pages, 5 figures; "Dwarf Galaxies: Keys to Galaxy Formation and
Evolution" JENAM 2010 Symposium S
The stellar content of the Hamburg/ESO survey. V. The metallicity distribution function of the Galactic halo
We determine the metallicity distribution function (MDF) of the Galactic halo
by means of a sample of 1638 metal-poor stars selected from the Hamburg/ESO
objective-prism survey (HES). The sample was corrected for minor biases
introduced by the strategy for spectroscopic follow-up observations of the
metal-poor candidates, namely "best and brightest stars first". [...] We
determined the selection function of the HES, which must be taken into account
for a proper comparison between the HES MDF with MDFs of other stellar
populations or those predicted by models of Galactic chemical evolution. The
latter show a reasonable agreement with the overall shape of the HES MDF for
[Fe/H] > -3.6, but only a model of Salvadori et al. (2007) with a critical
metallicity for low-mass star formation of Z_cr = 10^{-3.4} * Z_Sun reproduces
the sharp drop at [Fe/H] ~-3.6 present in the HES MDF. [...] A comparison of
the MDF of Galactic globular clusters and of dSph satellites to the Galaxy
shows qualitative agreement with the halo MDF, derived from the HES, once the
selection function of the latter is included. However, statistical tests show
that the differences between these are still highly significant. [ABSTRACT
ABRIDGED]Comment: Accepted for publication in A&