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We predict the frequency distribution of elemental abundance ratios from Carbon to Zinc as a functions of time location, which can be directly compared with the next generation of the galactic archeology project such as the HERMES. We perform the chemodynamical simulations of a Milky Way-type galaxy from a CDM initial condition, using a self-consistent hydrodynamical code with supernova feedback chemical enrichment. In the simulated galaxy, the kinematical and chemical properties of the bulge, disk, halo are consistent with the observations. The bulge have formed from the assembly of subgalaxies at z>=2, and have higher [α/Fe] ratios because of the lack of contribution of Type Ia Supernovae. The disk have formed with a constant star formation over 13 Gyr shows a decreasing trend of [α/Fe] and increasing trends of [(Na, Al, Cu, Mn)/Fe]. However, the thick disk stars tend to have higher [α/Fe] lower [Mn/Fe] than thin disk stars. 60% of the thick disk stars have formed in the satellite galaxies before they accrete on the disk in this CDM-based simulation. [ABSTRACT FROM AUTHOR]

Dark matter plays a fundamental role in theories of formation and evolution of galaxies, so every attempt to model galaxy formation and evolution has to consider the presence of dark halos. Moreover, mergers and accretions appear to be fundamental driving mechanisms in determining the present day properties of galaxies. Our project studies the ultra-fine distribution of dark matter in the Milky Way and the implications for the next generation of dark matter particle detectors. We have developed a model for halo mergers in a Milky Way-like galaxy. The signals expected in the lab-based dark matter detection experiments depend on the phase-space distribution on submilliparsec scales: with our numerical technique it is possible to resolve structures, produced by mergers of subhalos with a larger parent halo, inaccessible to conventional N-body simulations. When applied in a cosmological context, this method becomes a powerful instrument to reproduce and analyse the complete multiple merger history of a Milky Way-like system. Preliminary results suggest that fine-grained features from mergers that occurred a few Gyrs ago survive until now. These features may raise also the possibility of using them to unravel the complete merger history of the Milky Way. [ABSTRACT FROM AUTHOR]

We are describing the main ingredients necessary to build galactic chemical evolution models and discuss their uncertainties. The predictions of such models are then compared to observational data and from this comparison we infer important constraints on the timescales for the chemical enrichment in galaxies as well as on the mechanisms of galaxy formation. Our results are also discussed in comparison with the hierarchical cosmological approach to galaxy formation. [ABSTRACT FROM AUTHOR]

The ACS Survey of Galactic Globular Clusters is a Hubble Space Telescope (HST) Treasury program designed to provide a new large, deep and homogeneous photometric database. Based on observations from this program, we have measured precise relative ages for a sample of 64 Galactic globular clusters by comparing the relative position of the clusters’ main sequence turn offs, using main-sequence fitting to cross-compare clusters within the sample. This method provides relative ages to a formal precision of 2–7%. We demonstrate that the calculated relative ages are independent of the choice of theoretical model. We find that the Galactic globular cluster sample can be divided into two groups—a population of old clusters with an intrinsic age dispersion of ∼3% and no age-metallicity relation, and a group of younger clusters with an age-metallicity relation similar to that of the globular clusters associated with the Sagittarius dwarf galaxy. These results are consistent with the Milky Way halo having formed in two phases. The first phase would be compatible with a rapid (<0.8 Gyr) assembling process of the halo, in which the clusters in the old group were formed. The second phase lasted much longer in time and resulted in a group of globular clusters with a clear age-metallicity relation. It is very tempting to argue that the origin of this second group of clusters is related to the accretion of Milky Way satellite galaxies, but the origin of the age-metallicity relation remains unclear. [ABSTRACT FROM AUTHOR]

Recent observational studies show considerable small dispersions for abundance ratios of C–Zn relative to iron in metal-poor halo stars. On the other hand, abundance ratios of neutron-capture elements show large scatters, suggesting incomplete mixing of the interstellar medium at the beginning of the Galaxy. We attempt to explain these contradictory observations, using an inhomogeneous chemical evolution model, which is shown to well reproduce large scatters in neutron-capture elements in our previous studies. In particular, taking into account of difference of observational trends among iron-peak elements, we discuss nucleosynthesis of the very first stars. [ABSTRACT FROM AUTHOR]

Theoretical models suggest that a transition from massive Population III stars to normal Population II/I stars occurs when the metallicity of the star forming gas crosses the critical range Zcr = 10-5±1 Z⊙. According to this view, the formation of Population III stars is regulated by the rate at which heavy elements are produced and mixed in the gas surrounding the first star-forming regions. The cosmic implications of such process, generally referred to as chemical feedback, have been investigated following semi-analytic approaches which have either focused on the transport of metals through supernova-driven outflows, or on the “genetic” transmission of metals from parent sub-halos along the hierarchical evolution of cosmic structures. Although the above studies find that it is difficult to rapidly suppress the formation of Pop III stars, this common wisdom has to face the fact that no metal-free stars have yet been found by surveys of metal-poor stars of the Milky Way halo. Alternative probes such as the apparent excess in the cosmic near-infrared background, the equivalent width distributions of high-z Lyα emitters, and the He II 1640 Å line in composite spectra of LBGs, are yielding only tentative evidence for the presence of Pop III stars at z<9. The question then remains: are Pop III stars hidden (due to their very small statistical frequency or because they reside in as-yet-unexplored environments) or did they disappear as a result of chemical feedback a long time ago? The work presented here attempts to address this question using numerical simulations which follow the evolution, metal enrichment and energy deposition of both Population III and Population II stars. [ABSTRACT FROM AUTHOR]

Observed large scatters in abundance ratios of neutron-capture elements relative to iron in metal-poor stars may suggest incomplete mixing of the interstellar medium at the beginning of the Galaxy. On the other hand, recent studies of metal-poor stars show considerable small dispersions for abundance ratios of C-Zn. We discuss whether such variations of scatters in abundance ratios can be explained by a consistent chemical evolution model. We also attempt to constrain the origins of r-process elements, comparing predictions by an inhomogeneous chemical evolution model with new observational results with Subaru HDS. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

We discuss the reliability of one of the most used method to determine the helium-to-metals enrichment ratio (ΔY/ΔZ), i.e. the photometric comparison of a selected data set of local disk low main sequence (MS) stars observed by Hipparcos with a new grid of stellar models with up-to-date input physics. Most of the attention has been devoted to evaluate the effects on the final results of different sources of uncertainty (observational errors, evolutionary effects, selection criteria, systematic uncertainties of the models, numerical errors). As a check of the result the procedure has been repeated using another, independent, data set: the low-MS of the Hyades cluster. The obtained ΔY/ΔZ for the Hyades, together with spectroscopic determinations of [Fe/H] ratio, have been used to obtain the Y and Z values for the cluster. Isochrones have been calculated with the estimated chemical composition, obtaining a very good agreement between the predicted position of the Hyades MS and the observational data in the color-magnitude diagram. [ABSTRACT FROM AUTHOR]