Chemical evolution models for dwarf metal poor galaxies, including dwarf irregulars and dwarf spheroidals will be presented. The main ingredients necessary to build detailed models of chemical evolution including stellar nucleosynthesis, supernova progenitors, stellar lifetimes and stellar feedback will be discussed. The stellar feedback will be analysed in connection with the development of galactic winds in dwarf galaxies and their effects on the predicted abundances and abundance ratios. Model results concerning α-elements (O, Mg, Si, Ca), Fe and s-and r-process elements will be discussed and compared with the most recent observational data for metal poor galaxies of the Local Group. We will show how the study of abundance ratios versus abundances can represent a very powerful tool to infer constraints on galaxy formation mechanisms. In this framework, we will discuss whether, on the basis of their chemical properties, the dwarf galaxies of the Local Group could have been the building blocks of the Milky Way.

We use Beryllium to investigate star formation in the early Galaxy. Be has been demonstrated to be a good indicator of time in these early epochs. By analyzing the so-far largest sample of halo and thick disk metal poor stars, we find a clear scatter in Be for a given value of [Fe/H] and [O/H]. The scatter is very pronounced for Halo stars, while it is marginal for thick disk stars. Our halo stars separate in the [α/Fe] - Be diagram, showing two main branches: one indistinguishable from the thick disk stars, and one with lower [α/Fe] ratio. The stars belonging to this branch are characterized by highly eccentric orbits and small perigalactic radius (Rmin). Their kinematics are consistent with an accreted component.

Gaia development is in full speed aiming to the launch in December 2011. While the entities formally responsible to make Gaia happen are very focused to be ready in time, it is necessary to explore the readiness of the wider scientific community to exploit Gaia data in the future. The GST sees a role for itself in building and enabling the community to use the Gaia catalogues when they become available. This paper gives the background for the current activities the GST is taking to promote the community to start preparations for the exploitation of Gaia data.

An overview is given of the chemical processes that occur in primordial systems under the influence of radiation, metal abundances and dust surface reactions. It is found that radiative feedback effects differ for UV and X-ray photons at any metallicity, with molecules surviving quite well under irradiation by X-rays. Starburst and AGN will therefore enjoy quite different cooling abilities for their dense molecular gas. The presence of a cool molecular phase is strongly dependent on metallicity. Strong irradiation by cosmic rays (>200× the Milky Way value) forces a large fraction of the CO gas into neutral carbon. Dust is important for H2 and HD formation, already at metallicities of 10−4 − 10−3 solar, for electron abundances below 10−3.

We present several results from our analysis of dwarf irregular galaxies culled from The HI Nearby Galaxy Survey (THINGS). We analyse the rotation curves of two galaxies based on “bulk” velocity fields, i.e. velocity maps from which random non–circular motions are removed. We confirm that their dark matter distribution is best fit by an isothermal halo model. We show that the star formation properties of dIrr galaxies resemble those of the outer parts of larger, spiral systems. Lastly, we study the large scale (3–D) distribution of the gas, and argue that the gas disk in dIrrs is thick, both in a relative, as well as in an absolute sense as compared to spirals. Massive star formation through subsequent supernova explosions is able to redistribute the bulk of the ISM, creating large cavities. These cavities are often larger, and longer–lived than in spiral galaxies.

Mass loss is a determinant factor which strongly affects the evolution and the fate of massive stars. At low metallicity, stars are supposed to rotate faster than at the solar one. This favors the existence of stars near the critical velocity. In this rotation regime, the deformation of the stellar surface becomes important, and wind anisotropy develops. Polar winds are expected to be dominant for fast rotating hot stars.

These polar winds allow the star to lose large quantities of mass and still retain a high angular momentum, and they modify the evolution of the surface velocity and the final angular momentum retained in the star's core. We show here how these winds affect the final stages of massive stars, according to our knowledge about Gamma Ray Bursts. Computation of theoretical Gamma Ray Bursts rate indicates that our models have too fast rotating cores, and that we need to include an additional effect to spin them down. Magnetic fields in stars act in this direction, and we show how they modify the evolution of massive star up to the final stages.

We study the evolution of the first stars in the universe (Population III) from the early pre–Main Sequence (MS) until the end of helium burning in the presence of WIMP dark matter annihilation inside the stellar structure. The two different mechanisms that can provide this energy source are the contemporary contraction of baryons and dark matter, and the capture of WIMPs by scattering off the gas with subsequent accumulation inside the star. We find that the first mechanism can generate an equilibrium phase, previously known as a dark star, which is transient and present in the very early stages of pre–MS evolution. The mechanism of scattering and capture acts later, and can support the star virtually forever, depending on environmental characteristics of the dark matter halo and on the specific WIMP model.

This paper presents the results of a study aimed at understanding the evolution of the dust properties, as a function of both the environmental conditions and the metal enrichment of the system. I first review the peculiar dust properties of dwarf galaxies, and discuss attempts to understand their origin. Then, I discuss the evolution of the PAH and dust abundances, constrained by the UV-to-radio SED of nearby galaxies, comparing the properties of low-metallicity environments and more evolved systems. I discuss the long term evolution of dust in galaxies, comparing the grain production by various stellar progenitors to their destruction by SN blast waves and in H ii regions. Finally, I will show how these models explain the paucity of PAHs in low-metallicity environments.

We have derived a complete magnitude-limited sample of 440 Galactic open clusters in the solar neighborhood, with integrated V-magnitude brighter than 8 mag. This sample can be used to infer the present-day luminosity and mass functions of open clusters up to a given age; it can even be used to construct the initial mass and luminosity function (IMF, ILF) of clusters (defined as visible clusters with age 4 – 8 Myr). The high-mass end of the cluster IMF is a power-law with a slope of −2 or slightly shallower (−1.7) while the luminous cluster ILF has a power-slope of −1, in agreement with what is found for extragalactic clusters. Both distribution functions show a turnover, starting at 300 M⊙ and integrated magnitude −3 mag, respectively. The overall birthrate of clusters is 0.4 clusters per kpc2 and per Myr. The average present-day cluster mass is 700 M⊙, while the average initial cluster mass is 4500 M⊙. The difference of these two average masses indicates the high infant mortality and/or weight loss of Galactic open clusters (due to dynamical evolution).

I discuss how the chemical abundance distributions, kinematics and age distributions of stars in the thin and thick disks of the Galaxy can be used to decipher the merger history of the Milky Way, a typical large galaxy. The observational evidence points to a rather quiescent past merging history, unusual in the context of the ‘consensus’ cold-dark-matter cosmology favoured from observations of structure on scales larger than individual galaxies.

We review the current state of knowledge of damped Lyα systems (DLAs) selected in absorption on quasar sightlines. These objects are extremely useful to study the interstellar medium of high-redshift galaxies and the nucleosynthesis in the early Universe. The characteristics of this galaxy population has been investigated for years and slowly we are getting information on their puzzling nature. Imaging at z <1 shows that DLAs are associated with a mixing bag of galaxies with no especially large contribution from dwarf galaxies. Evidence for a mild evolution of the cosmic mean metallicity with time is observed. The star formation histories of these high-redshift galaxies begin to be accessible and indicate that DLAs tend to be young, gas-dominated galaxies with low star formation rates per unit area. Finally, indirect estimation of the DLA stellar masses from the mass-metallicity relations observed for emission-selected star-forming galaxies at z = 2−3 points to intermediate-mass galaxies with M* < 109M⊙.

We test the hypothesis that the host galaxies of long-duration gamma-ray bursts (GRBs) as well as quasar-selected damped Lyman-α (DLA) systems are drawn from the population of UV-selected star-forming, high z galaxies (generally referred to as Lyman-break galaxies). Specifically, we compare the metallicity distributions of the GRB and DLA populations against simple disk models where these galaxies are drawn randomly from the distribution of star-forming galaxies according to their star-formation rate and HI cross-section respectively. We find that it is possible to match both observational distributions assuming very simple and constrained relations between luminosity, metallicity, metallicity gradients and HI sizes. The simple model can be tested by observing the luminosity distribution of GRB host galaxies and by measuring the luminosity and impact parameters of DLA selected galaxies as a function of metallicity. Our results support the expectation that GRB and DLA samples, in contrast with magnitude limited surveys, provide an almost complete census of star-forming galaxies at z ≈ 3.

An important open frontier in astrophysics is to understand how the first sources of light, the first stars and galaxies, ended the cosmic dark ages at redshifts z ≃ 15 − 20. Their formation signaled the transition from the simple initial state of the universe to one of ever increasing complexity. We here review recent progress in understanding the assembly process of the first galaxies with numerical simulations, starting with cosmological initial conditions and modelling the detailed physics of star formation. The key drivers in building up the primordial galaxies are the feedback effects from the first stars, due to their input of radiation and of heavy chemical elements in the wake of supernova explosions. In addition, the conditions inside the first galaxies are governed by the gravitationally-driven turbulence generated during the virialization of the dark matter host halo. Our theoretical predictions will be tested with upcoming near-infrared observatories, such as the James Webb Space Telecope, in the decade ahead.

The successful implementation of integral field near-infrared spectrographs fed by adaptive optics is providing unprecedented views of gas motions within galaxies at redshifts z = 2 − 3, when the universe was forming stars at its peak rate. A complex picture of galaxy kinematics is emerging, with inflows, rotation within sometimes extended and nearly always thick disks, mergers, and galaxy-wide outflows all contributing to the variety of patterns seen. On the computational side, simulations of galaxy formation have reached a level of sophistication which can not only reproduce many of the properties of today's galaxies, but also throws new light on high redshift galaxies which are too faint to be detected directly, such as those giving rise to quasar absorption lines. In this brief review, I summarise recent progress in these areas.

Blue Compact Dwarf (BCD) galaxies are the most metal-deficient star-forming galaxies known in the universe, with metallicities ranging from 1/40 to 1/3 that of the Sun. I review how they constitute excellent nearby laboratories for studying big bang nucleosynthesis and star formation and galaxy evolution processes in a nearly primordial environment.

Recent data have revealed a clear distinction between the abundance patterns of the Milky Way (MW) thick and thin disks, suggesting a different origin for each of these components. In this work we first review the main ideas on the formation of the thin disk. From chemical evolution arguments we show that the thin disk should have formed on a long timescale. We also show clear signs that the local stellar samples are contaminated by stars coming from inner radii. We then check what would have to be changed in such a model in order to explain the observables in the thick disk. We find that a model in which the thick disk forms on a much shorter timescale than thin disk and with a star formation efficiency of around a factor of 10 larger than that in the thin disk can account for the observed abundance ratio shifts of several elements between thick and thin disk stars. Moreover, the lack of scatter in the abundance ratio patterns of both the thick and thin disks suggest both components to have been formed in situ by gas accretion and not by mergers of smaller stellar systems. Especially for the thick disk, this last constraint becomes a strong one if its metallicity distribution extends to, at least, solar. Finally, we briefly discuss the interplay between present deuterium abundance and present infall rates in connection with the thin disk evolution.

We consider the fragmentation mass scale of low-metallicity clouds based on their thermal evolution. Then we present the protostellar evolution in the main accretion phase, and discuss the upper limit on the stellar mass by the stellar feedback.

Current numerical studies suggest that the first protogalaxies formed a few stars at a time and were enriched only gradually by the first heavy elements. However, these models do not resolve primordial supernova (SN) explosions or the mixing of their heavy elements with ambient gas, which could result in intervening, prompt generations of low-mass stars. We present multiscale 1D models of Population III supernovae in cosmological minihalos that evolve the blast from its earliest stages as a free expansion. We find that if the star ionizes the halo, the ejecta strongly interacts with the dense shell swept up by the H II region, potentially cooling and fragmenting it into clumps that are gravitationally unstable to collapse. If the star fails to ionize the halo, the explosion propagates metals out to 20 - 40 pc and then collapses, heavily enriching tens of thousands of solar masses of primordial gas, in contrast to previous models that suggest that such explosions ‘fizzle’. Rapid formation of low-mass stars trapped in the gravitational potential well of the halo is unavoidable in these circumstances. Consequently, it is possible that far more stars were swept up into the first galaxies, at earlier times and with distinct chemical signatures, than in present models. Upcoming measurements by the James Webb Space Telescope (JWST) and Atacama Large Millimeter Array (ALMA) may discriminate between these two paradigms.

Disk galaxies are common in our universe and this is a source of concern for hierarchical formation models like ΛCDM. Here we investigate this issue as motivated by raw merger statistics derived for galaxy-size dark matter halos from ΛCDM simulations. Our analysis shows that a majority (~ 70%) of galaxy halos with M0 = 1012M⊙ at z = 0 should have accreted at least one object with mass m > 1011M⊙ ≃ 3 Mdisk over the last 10 Gyr. Mergers involving larger objects m ≳ 3 × 1011M⊙ should have been very rare for Milky-Way size halos today, and this pinpoints m/M ~ 0.1 mass-ratio mergers as the most worrying ones for the survival of thin galactic disks. Motivated by these results, we use use high-resolution, dissipationless N-body simulations to study the response of stellar Milky-Way type disks to these common mergers and show that thin disks do not survive the bombardment. The remnant galaxies are roughly three times as thick and twice as kinematically hot as the observed thin disk of the Milky Way. Finally, we evaluate the suggestion that disks may be preserved if the mergers involve gas-rich progenitors. Using empirical measures to assign stellar masses and gas masses to dark matter halos as a function of redshift, we show that the vast majority of large mergers experienced by 1012M⊙ halos should be gas-rich (fgas > 0.5), suggesting that this is a potentially viable solution to the disk formation conundrum. Moreover, gas-rich mergers should become increasingly rare in more massive halos > 1012.5M⊙, and this suggest that merger gas fractions may play an important role in establishing morphological trends with galaxy luminosity.

To date, fully cosmological hydrodynamic disk simulations to redshift zero have only been undertaken with particle-based codes, such as GADGET, Gasoline, or GCD+. In light of the (supposed) limitations of traditional implementations of smoothed particle hydrodynamics (SPH), or at the very least, their respective idiosyncrasies, it is important to explore complementary approaches to the SPH paradigm to galaxy formation. We present the first high-resolution cosmological disk simulations to redshift zero using an adaptive mesh refinement (AMR)-based hydrodynamical code, in this case, RAMSES. We analyse the temporal and spatial evolution of the simulated stellar disks' vertical heating, velocity ellipsoids, stellar populations, vertical and radial abundance gradients (gas and stars), assembly/infall histories, warps/lopsideness, disk edges/truncations (gas and stars), ISM physics implementations, and compare and contrast these properties with our sample of cosmological SPH disks, generated with GCD+. These preliminary results are the first in our long-term Galactic Archaeology Simulation program.