We have developed in GADGET-2 a feature–rich and highly flexible code for modeling the stellar evolution and the chemical enrichment. Simulating clusters, we find a very good agreement in reproducing both the radial abundance profiles and the enrichment history of the Intra–Cluster medium.

I review the current status of the comparison between observational properties of galaxy clusters and predictions from cosmological hydrodynamical simulations. My presentation focuses on the thermodynamical and chemical properties of the intra–cluster medium (ICM), as observed in the X–ray band. I finally discuss the properties of the galaxy population and their relation with the those of the hot diffuse gas. The emerging picture highlights that the current numerical description of galaxy clusters is able to account for several properties, such as the slope of the temperature profiles outside the core regions, the global chemical enrichment of the ICM and the color and luminosities for the bulk of the galaxy population. However, important discrepancies between observations and simulations are found, such as the thermal structure of cool cores and the colors of the brightest cluster galaxies. I emphasize that such two failures are two faces of the same problem, namely the difficulty of regulating gas cooling and star formation inside the most massive dark matter halos. This calls for the need of a source of energy feedback, which is not directly related to star formation, thus pointing towards AGN as a natural candidate for such a mechanism.

We use cosmological hydrodynamic simulations including galacticfeedback based on observations of local starbursts to find aself-consistent evolutionary model capable of fitting the observationsof the intergalactic metallicity history as traced by C iv betweenz = 6.0 → 1.5. Our main finding is that despite the relativeinvariance in the measurement of Ω(C iv) as well as the columndensity and linewidth distributions over this range, continualfeedback from star formation-driven winds are able to reproduce theobservations, while an early enrichment scenario where a majority ofthe metals are injected into the IGM at z > 6 is disfavored. Theconstancy of the C iv observations results from a rising IGMmetallicity content balanced by a declining C iv ionization fractiondue to a 1) decreasing physical densities, 2) increasing ionizationbackground strength, and 3) metals becoming more shock-heated at lowerredshift. Our models predict that ~20× more metals areinjected into the IGM between z = 6 → 2 than at z > 6. Weshow that the median C iv absorber at z = 2 traces metals injected 1 Gyr earlier indicating that the typical metals traced by C iv areneither from very early times nor from very recent feedback.


The enrichment of the intergalactic medium with heavy elements is aprocess that lies at the nexus of poorly-understood aspects ofphysical cosmology. We review current understanding of the processesthat may remove metals from galaxies, the basic predictions of thesemodels, the key observational constraints on enrichment, and howintergalactic enrichment may be used to test cosmological simulations.


In this article I briefly review recent abundance measurements in intermediate- and high-velocity clouds (IVCs and HVCs, respectively) in the halo of the Milky Way. FUSE and STIS absorption line data indicate that these clouds span a metallicity range between ~0.1−1.0 solar, suggesting that they cannot have asingle origin. Most likely, the infall of gas from the intergalactic medium and from satellite galaxies is responsible for the population of low-metallicity HVCs like Complex C, whilethe more metal-rich clouds (in particular the IVCs) representGalactic material as part of a galactic fountain.The detailed analysis of particularly interesting ionsand molecules (e.g., O i, D i, N i, O vi, andH2) gives a detailed insight into the chemical compositionof individual clouds and further provides important information onthe physical conditions in these objects.

We use cosmological hydrodynamic simulations with enriched galacticoutflows to compare predictions for the galaxy mass-metallicity (M* − Z)with observations at z ≈ 2 from Erb et al. (2006). With no outflowsincluded galaxies are over-enriched, indicating that outflows are requirednot only to suppress star formation and enrich the IGM but also to lowergalaxy metal content. The observed M* − Z slope is matched both inour model without winds as well as in our favored outflow model where theoutflow velocity scales as the escape velocity, but is too steep ina model with constant outflow speeds. If outflows are too widespreadat early times, the IGM out of which smaller galaxies form can becomepre-polluted, resulting in a low-mass flattening of the M* − Z relationthat is inconsistent with data. Remarkably, the same momentum-drivenwind model that provides the best agreement with IGM enrichment dataalso yields the best agreement with the z ≈ 2 M* − Z relation,showing the proper outflow scaling and strength to match the observedslope and amplitude. In this model, the M* − Z relation evolves slowlyfrom z = 6 → 2; an (admittedly uncertain) extrapolation to z = 0broadly matches local M* − Z observations. Overall, the M* − Zrelation provides critical constraints on galactic outflow processesduring the heyday of star formation in the Universe.

I review the most widely used methods of determining chemicalabundances in galaxies at 1≲ z ≲ 3, including emission andabsorption line techniques (including a brief discussion of DampedLyman Alpha systems). Most star-forming galaxies at these redshiftsshow significant enrichment, with ~1/3 solar to ~solarmetallicities. They are overluminous for their metallicities comparedto local galaxies, and the mass-metallicity relation at z ~ 2 isoffset to lower metallicities compared to the local relation. Metalsare also seen in the IGM at these redshifts, most likely fromgalactic-scale outflows in the galaxies themselves.

A complementary method to the emission selection of high-redshiftgalaxies consists in the observation of absorbers along the line ofsight toward a background quasar. This selection technique has aconstant sensitivity at all redshifts up to z = 6 (i.e. no redshiftdesert) and allow to select all types of galaxies regardless of theirluminosity or star formation rate. The highest column densityabsorbers, the Damped Lyman-α (DLAs) systems, in particular,can be used to determine the cosmic evolution of HI gas in theUniverse, ΩHI, and the global metallicity in the gasphase. Since stars are known to form from HI gas, ΩHIprovides an indirect tracer of the history of starformation. Recent results from several parallel VLT programmes aimingat determining the cosmological evolution of the metallicity in theneutral gas phase are presented.

The most metal-poor stars provide important constraints on a number of problems, including the modeling of the early stages of galaxy assembly, the nature of first stars and the reionization. I present here numerical results on the distribution of metal-poor stars in stellar halos formed in a ΛCDM cosmology. I then discuss the results in light of current observational data of very metal-poor stars in the halos of Milky Way, Andromeda and neighboring dwarf galaxies.


This contribution addresses the issue of metal enrichment and the distribution of metals in the ISM/IGM/ICM within the framework of a hybrid N-body plus semi-analytic method. It discusses its impact on galaxy bimodality and multi-wavelength galaxy counts.

We report an ultra-high-resolution simulation that follows evolution from the earliest stages of galaxy formation through the period of dynamical relaxation. The bubble structures of gas revealed in our simulation (<3×108 years) resemble closely the high-redshift Lyman α emitters (LAEs). After 109 years these bodies are dominated by stellar continuum radiation and look like the Lyman break galaxies (LBGs) known as the high-redshift star-forming galaxies at which point the abundance of elements appears to be solar. After 1.3×1010 years, these galaxies resemble present-day ellipticals. The comparisons of simulation results with the observations of elliptical galaxies allow us to conclude that LAEs and LBGs are infants of elliptical galaxies or bulge systems in the nearby universe.

Feedback processes are now realized to hold the key to our understanding ofgalaxy formation and evolution, particularly during the early epochs that we commonly dub as the Cosmic Dawn. We propose and discuss a classification in which three broad feedback classes (radiative, chemical and mechanical) can be identified. We also discuss the underlying physics for each of these feedbacks and point outtheir importance in different cosmological contexts. Finally, the link between mechanical feedback and the heavy element transport is explored with the aim of understanding the cosmic metal budget and the enrichment history of the intergalactic medium.

We simulate cosmic chemical enrichment with a hydrodynamical model including supernova and hypernova feedback.We find that the majority of stars in present-day massive galaxies formed in much smaller galaxies at high redshifts, despite their late assembly times. The hypernova feedback drives galactic outflows efficiently in low mass galaxies, and these winds eject heavy elements into the intergalactic medium. The ejected baryon fraction is larger for less massive galaxies, correlates well with stellar metallicity.The observed mass-metallicity relation is well reproduced as a result of the mass-dependent galactic winds.We also predict the cosmic supernova and gamma-ray burst rate histories.

The advent of 8  m class telescopes has allowed the detailed spectroscopicstudy of sizeable numbers of extremely metal-poor Galactic stars whichare the witnesses of the formation of the early Galaxy. Their chemicalcomposition displays some distinctive trends which should providea strong constraint on the physical nature of the first generation(s) ofstars and on their nucleosynthetic output. I will review recent results in the field following the periodic table, from lithium to uranium andshortly comment on the intriguing classes of Carbon Enhanced Metal Poor (CEMP) stars, for many of which there is no analogue among solar metallicity stars. In spite of these exciting results, the number of known stars of metallicity below [Fe/H] = -3.3 remains quite small and it would be desirable to discover more, both to clearly understand the metal-weak tail of Halo metallicity distribution and to clarify the abundance trends at the lowest metallicities. Most of these extremely rare objects have been discovered by the wide field objective prism surveys, HK survey and Hamburg-ESO survey.In the near future the Sloan Digital Sky Survey and its continuation SEGUE are expected to boost significantly the numbers of known extremely metal poor stars. We are living exciting times but an even more exciting futurelies ahead!

Although the theoretical study of very low metallicity (Z) and metal–free stars is not new,their importance has recently greatly increased since two related fields have been developing rapidly. The first iscosmological simulations of the formation of the first stars and of the reionisation period. The second is the observations of extremely metal poor stars. In this paper, we present pre–supernova evolution models of massive rotating stars at very low Z (Z = 10-8) and at Z = 0. Rotation has astrong impact on mass loss and nucleosynthesis. Models reaching break–upvelocities lose up to ten percents of their initial mass.In very low Z models, rotational and convective mixing enhancessignificantly the surface content in carbon, nitrogen and oxygen (CNO)when the star becomes a red supergiant. This induces a strong massloss for stars more massive than about 60 M๏. Our models predict typeIb,c supernovae and gamma–ray bursts at very low Z. Rotational mixingalso induces a large production of CNO elements, in particular ofprimary nitrogen. The stellar wind chemical composition is compatible with themost metal–poor star know to date, HE 1327–2326, for CNO elements. Ourmodels reproduce the early evolution of nitrogen in the Milky Way.

The difference in density profiles of the contributions from different density peaks to dark matter halos results in certain expectations about the Milky Way's stellar halo. We cut our simulated halo stars into two populations: those forming before/during the last major merger, and those accreted after the last major merger. The former population are more centrally located at z = 0, while stars forming in low mass late forming proto-galaxies are spread through the halo. A difference in observed binding energy distinguishes these two populations. We look at possible chemical abundance signatures of the two populations. We also show that galaxies forming in isolated low σ peaks will form from primordial material. Thus, even though the oldest stars are centrally concentrated as they originated in the early collapsing, densest regions, primordial stars would be found distributed throughout the halo. Thus, the lack of observed metal free stars can be taken as directly constraining the Population III IMF, and the lowest metallicity observed stars can be interpreted as holding clues to the chemical yields of Pop III stars.


We observed nearby (D < 10 Mpc)galaxies (Henize 2-10, IC 10, IC 342, M 83, NGC 253 and NGC 6946) inthe rotational lines of carbon monoxide CO and in the fine-structuretransitions of atomic carbon [CI] with the Caltech SubmillimeterObservatory (CSO). Using our new data, those from the literature and theLVG and PDR models, we derived the physical properties of the warmand dense molecular gas (kinetic temperature, UV radiation field, gasdensity...) in each nucleus. We predicted lines intensities for the12CO(5-4), 12CO(7-6) and 12CO(8-7) lines which are,even now, still difficult or impossible to detect from the ground butwill become available in few years with ALMA and HIFI or PACS, on boardthe Herschel satellite. Studying the ISM of nearby galaxies, we providea first step in the understanding of the ISM processes in more distantgalaxies.

We combine CaII/NaI absorption and HI 21 cm emission line measurements to analyse the metal abundances, the distribution, the small-scale structure, and the physical conditions of intermediate- and high-velocity gas in the Galactic halo.


Galaxy properties in general and properties of host galaxies ofgamma-ray bursts (GRBs) in particular are investigated, usingN-body/Eulerian hydrodynamic simulations and the stellar populationsynthesis model, Starburst99. We identify simulated galaxiesthat have optical star formation rate and SFR-to-luminosity ratiosimilar to those observed in a well-defined sample of ten hostgalaxies. The specific rates of the numerical counterparts are equalto or higher than the median values estimated at the differentredshifts. At intermediate redshift, our overall population shows thatthe faintest and bluest galaxies are also the objects with the highestspecific rates. These results suggest that GRB host galaxies arelikely to be drawn from the high specific SFR sub-population ofgalaxies, rather than the high SFR galaxy population.


We have designed an analytical model for the evolutionof anisotropic galactic outflows. Theseoutflows follow the path of least resistance, and thustravel preferentially into low-density regions, away from cosmologicalstructures where galaxies form. We show thatanisotropic outflows can significantly enrich low-densitysystems with metals.