23 research outputs found
Limits on Pop III star formation with the most iron-poor stars
We study the impact of star-forming mini-haloes, and the Initial Mass
Function (IMF) of Population III (Pop III) stars, on the Galactic halo
Metallicity Distribution Function (MDF) and on the properties of C-enhanced and
C-normal stars at [Fe/H]<-3. For our investigation we use a data-constrained
merger tree model for the Milky Way formation, which has been improved to
self-consistently describe the physical processes regulating star-formation in
mini-haloes, including the poor sampling of the Pop III IMF. We find that only
when star-forming mini-haloes are included the low-Fe tail of the MDF is
correctly reproduced, showing a plateau that is built up by C-enhanced
metal-poor (CEMP) stars imprinted by primordial faint supernovae. The
incomplete sampling of the Pop III IMF in inefficiently star-forming
mini-haloes (< /yr) strongly limits the formation of Pair
Instability Supernovae (PISNe), with progenitor masses =[140-260] , even when a flat Pop III IMF is assumed.
Second-generation stars formed in environments polluted at >50% level by PISNe
are thus extremely rare, corresponding to 0.25% of the total stellar
population at [Fe/H]<-2, which is consistent with recent observations. The
low-Fe tail of the MDF strongly depends on the Pop III IMF shape and mass
range. Given the current statistics, we find that a flat Pop III IMF model with
=[10-300] is disfavoured by observations. We present
testable predictions for Pop III stars extending down to lower masses, with
=[0.1-300] .Comment: 15 pages, 11 figures. Accepted for publication in MNRAS. The only
change is the correction of a mistake in the list of author
Galaxy formation with radiative and chemical feedback
Here we introduce GAMESH, a novel pipeline which implements self-consistent
radiative and chemical feedback in a computational model of galaxy formation.
By combining the cosmological chemical-evolution model GAMETE with the
radiative transfer code CRASH, GAMESH can post process realistic outputs of a
N-body simulation describing the redshift evolution of the forming galaxy.
After introducing the GAMESH implementation and its features, we apply the code
to a low-resolution N-body simulation of the Milky Way formation and we
investigate the combined effects of self-consistent radiative and chemical
feedback. Many physical properties, which can be directly compared with
observations in the Galaxy and its surrounding satellites, are predicted by the
code along the merger-tree assembly. The resulting redshift evolution of the
Local Group star formation rates, reionisation and metal enrichment along with
the predicted Metallicity Distribution Function of halo stars are critically
compared with observations. We discuss the merits and limitations of the first
release of GAMESH, also opening new directions to a full implementation of
feedback processes in galaxy formation models by combining semi-analytic and
numerical methods.Comment: This version has coloured figures not present in the printed version.
Submitted to MNRAS, minor revision
Decoding the stellar fossils of the dusty Milky Way progenitors
We investigate the metallicity distribution function (MDF) in the Galactic halo and the relative fraction of carbon-normal and carbon-rich stars. To this aim, we use an improved version of the semi-analytical code GAlaxy MErger Tree and Evolution (GAMETE), that reconstructs the hierarchical merger tree of the Milky Way (MW), following the star formation history and the metal and dust evolution in individual progenitors. The predicted scaling relations between the dust, metal and gas masses for MW progenitors show a good agreement with observational data of local galaxies and of gamma-ray burst (GRB) host galaxies at 0.1 140 M&sun;, into the Pair-Instability SN progenitor mass range. The relative contribution of C-normal and C-enhanced stars to the MDF and its dependence on [Fe/H] points to a scenario where the Pop III/II transition is driven by dust cooling, and the first low-mass stars form when the dust-to-gas ratio in their parent clouds exceeds a critical value of {\cal D}_crit = 4.4 × 10^{-9}. Other transition criteria do not predict any C-normal stars below [Fe/H] < -4, at odds with observations
Sumário do Vol. 6, nº2 (2010)
We investigate the metallicity distribution function (MDF) of the Galactic halo and the relative fraction of Carbon-normal and Carbon-rich stars using the semi-analytical code GAMETE. The code reconstructs the hierarchical merger tree of the Milky Way (MW) and follows the star formation history and the metal evolution in individual progenitors, including for the first time the formation and evolution of dust. We predict scaling relations between the dust, metal and gas masses for MW progenitors and compare them with observational data of galaxies at
The history of the dark and luminous side of Milky Way-like progenitors
International audienceHere we investigate the evolution of a Milky Way (MW)-like galaxy with the aim of predicting the properties of its progenitors all the way from z ∼ 20 to z = 0. We apply gamesh to a high-resolution N-body simulation following the formation of a MW-type halo and we investigate its properties at z ∼ 0 and its progenitors in 0  6 the contribution of star-forming minihaloes is comparable to the star formation rate along the MW merger tree. These systems might then provide an important contribution in the early phases of reionization. A large number of minihaloes with old stellar populations, possibly Population III stars, are dragged into the MW or survive in the Local Group. At low redshift dynamical effects, such as halo mergers, tidal stripping and halo disruption redistribute the baryonic properties among halo families. These results are critically discussed in light of future improvements including a more sophisticated treatment of radiative feedback and inhomogeneous metal enrichment