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.