Context. Zinc in stars is an important reference element because it is a proxy to Fe in studies of damped Lyman-α systems (DLAs), permitting a comparison of chemical evolution histories of bulge stellar populations and DLAs. In terms of nucleosynthesis, it behaves as an alpha element because it is enhanced in metal-poor stars. Abundance studies in different stellar populations can give hints to the Zn production in different sites. Aims. The aim of this work is to derive the iron-peak element Zn abundances in 56 bulge giants from high resolution spectra. These results are compared with data from other bulge samples, as well as from disk and halo stars, and damped Lyman-α systems, in order to better understand the chemical evolution in these environments. Methods. High-resolution spectra were obtained using FLAMES+UVES on the Very Large Telescope. We computed the Zn abun-

Dark energy is the invisible fuel that seems to drive the current acceleration of the Universe. Its presence, which is inferred from an impressive convergence of high-quality observational results along with some apparently sucessful theoretical predictions, is also supported by the current estimates of the age of the Universe from dating of local and high-$z$ objects. In this paper we test the viability of several dark energy scenarios in the light of the age estimates of the high redshift ($z=3.91$) quasar APM 08279+5255. Using a chemodinamical model for the evolution of spheroids, we first reevaluate its current estimated age, as given by Hasinger et al. (2002). An age of 2.1 Gyr is set by the condition that Fe/O abundance ratio (normalized to solar values) of the model reaches 3.3, which is the best fit value obtained in the above reference. It is shown that for the currently accepted value of the matter density parameter, most of the existing dark energy scenarios cannot accomodate this old high redshift object unless the Hubble parameter is as low as $H_o = 58$ $\rm{km.s^{-1}.Mpc^{-1}}$, as recently advocated by Sandage and collaborators. Even considering less stringent age limits, only cosmological models that predicts a considerably old Universe at high-$z$ can be compatible with the existence of this object. This is the case of the conventional $\Lambda$CDM scenario and some specific classes of brane world cosmologies.Comment: 7 pages, 3 figures, uses mn.cl

We present the results of a numerical code that combines multi-zone chemical evolution with 1-D hydrodynamics to follow in detail the evolution and radial behaviour of gas and stars during the formation of elliptical galaxies. We use the model to explore the links between the evolution and formation of elliptical galaxies and QSO activity. The knowledge of the radial gas flows in the galaxy allows us to trace metallicity gradients, and, in particular, the formation of a high-metallicity core in ellipticals. The high-metallicity core is formed soon enough to explain the metal abundances inferred in high-redshift quasars. The star formation rate and the subsequent feedback regulate the episodes of wind, outflow, and cooling flow, thus affecting the recycling of the gas and the chemical enrichment of the intergalactic medium. The evolution of the galaxy shows several stages, some of which are characterized by a complex flow pattern, with inflow in some regions and outflow in other regions. All models, however, exhibit during their late evolution a galactic wind at the outer boundary and, during their early evolution, an inflow towards the galaxy nucleus. The inner inflow evolution could explain the bolometric luminosity of a quasar lodged at the galaxy centre as well as the evolution of the QSO luminosity function.Comment: 19 pages, 9 figures, to be published in MNRA

We use a simple model of spheroid formation to explore the relationship between the creation of stars and dust in a massive protogalaxy and the growth of its central black hole. This model predicts that submillimetre luminosity peaks after only ≃0.2 Gyr. However, without a very massive seed black hole, Eddington‐limited growth means that a black hole mass of 109 M⊙, and hence very luminous active galactic nuclei (AGN) activity, cannot be produced until >0.5 Gyr after the formation of the first massive stars in the halo. The model thus predicts a time‐lag between the peak of submillimetre luminosity and AGN luminosity in a massive protoelliptical of a few times 108 yr. For a formation redshift z≃ 5, this means that powerful AGN activity is delayed until z≃ 3.5, by which time star formation in the host is ≃90 per cent complete, and submillimetre luminosity has declined to ≃25 per cent of its peak value. This provides a natural explanation for why successful submillimetre detections of luminous radio galaxies are largely confined to z > 2.5. Conversely the model also predicts that while all high‐redshift luminous submillimetre‐selected sources should contain an active (and growing) black hole, the typical luminosity of the AGN in such objects is ≃1000 times smaller than that of the most powerful AGN. This is consistent with the almost complete failure to detect submillimetre selected galaxies with existing X‐ray surveys. Finally, the model yields a black hole–spheroid mass ratio, which evolves rapidly in the first Gyr, but asymptotes to ≃0.001–0.003 in agreement with results at low redshift. This ratio arises not because the AGN terminates star formation, but because fuelling of the massive black hole is linked to the total mass of gas available for star formation in the host.

It has recently been argued that single-collapse high-redshift models for elliptical galaxy formation can be rejected because they predict large numbers of very red galaxies at intermediate redshifts which are not seen in deep optical-infrared surveys. We argue, however, that this conclusion is premature since, while much effort has been invested in refining the predictions of hierarchical CDM models, only very simplistic models have been used to study the evolution of galaxies in other cosmogonies (e.g. isocurvature models). We demonstrate that the use of a more realistic multi-zone chemo-dynamical single-collapse model, yields colours at intermediate redshifts which are much bluer than inferred from the one-zone model, and indeed are comparable to those predicted by hierarchical merging despite still allowing $> 90%$ of the final stellar mass of elliptical galaxies to be formed in the first Gyr of their evolution. We, therefore, conclude that the one-zone model should be avoided to predict the colours of high-redshift galaxies and that the use of realistic multi-zone models allows the existence of ellipticals at high redshift, being their dismissal premature.Comment: Submitted to MNRA

Aims. Globular clusters are tracers of the history of star formation and chemical enrichment in the early Galaxy. Their abundance pattern can help understanding their chemical enrichment processes. In particular, the iron-peak elements have been relatively little studied so far in the Galactic bulge. Methods. The main aim of this work is to verify the strength of abundances of iron-peak elements for chemical tagging in view of identifying different stellar populations. Besides, the nucleosynthesis processes that build these elements are complex, therefore observational data can help constraining theoretical models, as well as give hints on the kinds of supernovae that enriched the gas before these stars formed.Results. The abundances of iron-peak elements are derived for the sample clusters, and compared with bulge field, and thick disk stars. We derive abundances of the iron-peak elements Sc, V, Mn, Cu, and Zn in individual stars of five bulge globular clusters (NGC 6528, NGC 6553, NGC 6522, NGC 6558, HP 1), and of the reference thick disk/inner halo cluster 47 Tucanae (NGC 104). High resolution spectra were obtained with the UVES spectrograph at the Very Large Telescope over the years.Conclusions. The sample globular clusters studied span metallicities in the range -1.2 < ∼ [Fe/H] < ∼ 0.0. V and Sc appear to vary in lockstep with Fe, indicating that they are produced in the same supernovae as Fe. We find that Mn is deficient in metal-poor stars, confirming that it is underproduced in massive stars; Mn-over-Fe steadily increases at the higher metallicities due to a metallicity-dependent enrichment by supernovae of type Ia. Cu behaves as a secondary element, indicating its production in a weak-s process in massive stars. Zn has an alpha-like behaviour at low metallicities, which can be explained in terms of nucleosynthesis in hypernovae. At the metal-rich end, Zn decreases with increasing metallicity, similarly to the alpha-elements.

Analyses of the polycyclic aromatic hydrocarbon (PAH) feature profiles, especially the 6.2 µm feature, could indicate the presence of nitrogen incorporated in their aromatic rings. In this work, 155 predominantly starburst-dominated galaxies (including HII regions and Seyferts, for example), extracted from the Spitzer/IRS ATLAS project (Hernán-Caballero & Hatziminaoglou 2011), have their 6.2 µm profiles fitted allowing their separation into the Peeters' A, B and C classes (Peeters et al. 2002). 67% of these galaxies were classified as class A, 31% were as class B and 2% as class C. Currently class A sources, corresponding to a central wavelength near 6.22 µm, seem only to be explained by polycyclic aromatic nitrogen heterocycles (PANH, Hudgins et al. 2005), whereas class B may represent a mix between PAHs and PANHs emissions or different PANH structures or ionization states. Therefore, these spectra suggest a significant presence of PANHs in the interstellar medium (ISM) of these galaxies that could be related to their starburst-dominated emission. These results also suggest that PANHs constitute another reservoir of nitrogen in the Universe, in addition to the nitrogen in the gas phase and ices of the ISM.

The evolution of the metallicity of damped Lyman α systems (DLAs) is investigated in order to explore several scenarios for the nature of these systems. The observational data on chemical abundances of DLAs are analysed with robust statistical methods, and the abundances are corrected for dust depletion. The results of this analysis are compared with predictions of several classes of chemical evolution models describing a variety of scenarios for DLAs: one‐zone dwarf galaxy models, multizone disc models and chemodynamical models representing dwarf galaxies. In order to settle constraints for star formation time‐scales and metal production in DLAs, we compare the observational data on the [α/Fe] and [N/α] ratios to the predictions from the models. In DLAs, these ratios are only partially reproduced by the dwarf galaxy one‐zone model and by the disc model. On the other hand, the chemodynamical model for dwarf galaxies reproduces the properties of nearly all DLAs. The connection between the gas flow evolution and the star formation rate is the reason for the ability of this model in reproducing the range of abundance ratios seen in DLAs. The comparison of the observed [α/Fe] and [N/α] trends with the predictions of the chemodynamical model is used to derive the formation epoch of dwarf galaxies. The chemodynamical model predicts that dwarf galaxies make a significant contribution to the observed total neutral gas density in DLAs, and that this contribution is more important at high redshifts (z≳ 2–3). This is consistent with a scenario in which the DLA population is dominated by dwarf galaxies at high redshifts and by discs at lower redshifts. The relation between DLAs and Lyman break galaxies (LBGs) is investigated with chemodynamical models describing LBGs. Our results calls for a smoother progression in the evolutionary history of DLAs and LBGs rather than a sharp dichotomy between the two populations. LBGs and DLAs may constitute a sequence of increasing star formation rate, with the LBGs being systems with typically short star formation time‐scales (∼108 yr), and the DLAs having slower star formation. We also raise the possibility that we could be missing a whole population of high H i density column objects, with metallicities intermediate between those of DLAs and LBGs. Finally, we discuss the possibility that relying only on the observations of DLAs could lead to an underestimate of the metal content of the high‐redshift Universe.