The nature of Long-GRB host galaxies from chemical abundances

Gamma-ray bursts (GRBs) are the most energetic events after the Big Bang and they have been observed up to very high redshift. By means of measures of chemical abundances now available for the galaxies hosting such events,thought to originate from the explosion of very powerful supernovae (Type Ib/c), we have the opportunity to study the nature of these host galaxies. The aim of this paper is to identify the hosts of Long GRBs (LGRBs) observed both at low and high redshift to see whether the hosts can be galaxies of the same type observed at different cosmic epochs. We adopt detailed chemical evolution models for galaxies of different morphological type (ellipticals, spirals, irregulars) which follow the time evolution of the abundances of several chemical elements (H, He, $\alpha$-elements, Fe), and compare the results with the observed abundances and abundance ratios in galaxies hosting LGRBs. We find that the abundances and abundance ratios predicted by models devised for typical irregular galaxies can well fit the abundances in the hosts both at high and low redshift. We also find that the predicted Type Ib/c supernova rate for irregulars is in good agreement with observations. Models for spirals and particularly ellipticals do not fit the high-redshift hosts of LGRBs (DLA systems) nor the low redshift hosts: in particular, ellipticals cannot possibly be the hosts of gamma-ray-bursts at low redshift since they do not show any star formation, and therefore no supernovae Ib/c. We conclude that the observed abundance and abundance ratios in LGRBs hosts suggest that these hosts are irregular galaxies both at high and low redshift thus showing that the host galaxies belong to in an evolutionary sequence.Comment: 8 pages, 9 figures, two references adde

The Richness and Beauty of the Physics of Cosmological Recombination: The Contributions from Helium

The physical ingredients to describe the epoch of cosmological recombination are amazingly simple and well-understood. This fact allows us to take into account a very large variety of processes, still finding potentially measurable consequences. In this contribution we highlight some of the detailed physics that were recently studied in connection with cosmological hydrogen and helium recombination. The impact of these considerations is two-fold: (i) the associated release of photons during this epoch leads to interesting and unique deviations of the Cosmic Microwave Background (CMB) energy spectrum from a perfect blackbody, which, in particular at decimeter wavelength, may become observable in the near future. Despite the fact that the abundance of helium is rather small, it also contributes a sizeable amount of photons to the full recombination spectrum, which, because of differences in the dynamics of the helium recombinations and the non-trivial superposition of all components, lead to additional distinct spectral features. Observing the spectral distortions from the epochs of hydrogen and helium recombination, in principle would provide an additional way to determine some of the key parameters of the Universe (e.g. the specific entropy, the CMB monopole temperature and the pre-stellar abundance of helium), not suffering from limitations set by cosmic variance. Also it permits us to confront our detailed understanding of the recombination process with direct observational evidence. (ii) with the advent of high precision CMB data, e.g. as will be available using the Planck Surveyor or CMBpol, a very accurate theoretical understanding of the ionization history of the Universe becomes necessary for the interpretation of the CMB temperature and polarization anisotropies. (abridged)Comment: 16 pages, 11 figures, proceedings of the conference: "A Century of Cosmology: Past, Present and Future

Perspectives on metaphyseal conservative stems

Total hip replacement is showing, during the last decades, a progressive evolution toward principles of reduced bone and soft tissue aggression. These principles have become the basis of a new philosophy, tissue sparing surgery. Regarding hip implants, new conservative components have been proposed and developed as an alternative to conventional stems. Technical and biomechanical characteristics of metaphyseal bone-stock-preserving stems are analyzed on the basis of the available literature and our personal experience. Mayo, Nanos and Metha stems represent, under certain aspects, a design evolution starting from shared concepts: reduced femoral violation, non-anatomic geometry, proximal calcar loading and lateral alignment. However, consistent differences are level of neck preservation, cross-sectional geometry and surface finishing. The Mayo component is the most time-tested component and, in our hands, it showed an excellent survivorship at the mid-term follow-up, with an extremely reduced incidence of aseptic loosening (partially reduced by the association with last generation acetabular couplings). For 160 implants followed for a mean of 4.7 years, survivorship was 97.5% with 4 failed implants: one fracture with unstable stem, 1 septic loosening and 2 aseptic mobilizations. DEXA analysis, performed on 15 cases, showed a good calcar loading and stimulation, but there was significant lateral load transfer to R3–R4 zones, giving to the distal part of the stem a function not simply limited to alignment. Metaphyseal conservative stems demonstrated a wide applicability with an essential surgical technique. Moreover, they offer the options of a “conservative revision” with a conventional primary component in case of failure and a “conservative revision” for failed resurfacing implants

The role of dedicated instrumentation in total hip arthroplasty

Tissue-sparing surgery is a surgical strategy aimed to reduce tissue damage in joint replacement. This can be achieved by reducing soft tissue trauma, performing minimally invasive access routes and limiting bone removal with implantation of conservative prostheses. In order to facilitate mini-approaches, special instrumentation was developed to avoid impingement of the soft tissues and provide an easier and more correct placement of the components. We performed an analysis of the literature and a research of the instrumentation available today, to evaluate the actual utility of dedicated tools

The Age of Cluster Galaxies from Continuum Colors

We determine the age of 1,104 early-type galaxies in eight rich clusters ($z = 0.0046$ to $0.175$) using a new continuum color technique. We find that galaxies in clusters divide into two populations, an old population with a mean age similar to the age of the Universe (12 Gyrs) and a younger population with a mean age of 9 Gyrs. The older population follows the expected relations for mass and metallicity that imply a classic monolithic collapse origin. Although total galaxy metallicity is correlated with galaxy mass, it is uncorrelated with age. It is impossible, with the current data, to distinguish between a later epoch of star formation, longer duration of star formation or late bursts of star formation to explain the difference between the old and young populations. However, the global properties of this younger population are correlated with cluster environmental factors, which implies secondary processes, post-formation epoch, operate on the internal stellar population of a significant fraction of cluster galaxies. In addition, the mean age of the oldest galaxies in a cluster are correlated with cluster velocity dispersion implying that galaxy formation in massive clusters begins at earlier epochs than less massive clusters.Comment: 35 pages, 10 figures, accepted by Ap

The Ages, Metallicities and Alpha Element Enhancements of Globular Clusters in the Elliptical NGC 5128: A Homogeneous Spectroscopic Study with Gemini/GMOS

We present new integrated light spectroscopy of globular clusters (GCs) in NGC 5128 in order to measure radial velocities and derive ages, metallicities, and alpha-element abundance ratios. Using Gemini-S 8-m/GMOS, we obtained spectroscopy in the range of ~3400-5700 AA for 72 GCs with S/N > 30 /AA and we have also discovered 35 new GCs within NGC 5128 from our radial velocity measurements. We measured and compared the Lick indices from HdeltaA through Fe5406 with the single stellar population (SSP) models of Thomas et al.(2003,2004). We also measure Lick indices for 41 Milky Way GCs from Puzia et al. (2002) and Schiavon et al. (2005) with the same methodology for direct comparison. Our results show that 68% of the NGC 5128 GCs have old ages (> 8 Gyr), 14% have intermediate ages (5-8 Gyr), and 18% have young ages (< 5 Gyr). However, when we look at the metallicity of the GCs as a function of age, we find 92% of metal-poor GCs and 56% of metal-rich GCs in NGC 5128 have ages > 8 Gyr, indicating that the majority of both metallicity subpopulations of GCs formed early, with a significant population of young and metal-rich GCs forming later. Our metallicity distribution function generated directly from spectroscopic Lick indices is clearly bimodal, as is the color distribution of the same set of GCs. Thus the metallicity bimodality is real and not an artifact of the color to metallicity conversion. The [alpha/Fe] values are supersolar with a mean value of 0.14pm0.04, indicating a fast formation timescale. However, the GCs in NGC 5128 are not as [alpha/Fe] enhanced as the Milky Way GCs also examined in this study. Our results support a rapid, early formation of the GC system in NGC 5128, with subsequent major accretion and/or GC and star forming events in more recent times (abridged).Comment: Accepted to The Astrophysical Journal, 36 pages, 14 figures, 7 table

UVES/VLT high resolution spectroscopy of GRB 050730 afterglow: probing the features of the GRB environment

We analyze high resolution spectroscopic observations of the optical afterglow of GRB050730, obtained with UVES@VLT about hours after the GRB trigger. The spectrum shows that the ISM of the GRB host galaxy at z = 3.967 is complex, with at least five components contributing to the main absorption system. We detect strong CII*, SiII*, OI* and FeII* fine structure absorption lines associated to the second and third component. For the first three components we derive information on the relative distance from the site of the GRB explosion. Component 1, which has the highest redshift, does not present any fine structure nor low ionization lines; it only shows very high ionization features, such as CIV and OVI, suggesting that this component is very close to the GRB site. From the analysis of low and high ionization lines and fine structure lines, we find evidences that the distance of component 2 from the site of the GRB explosion is 10-100 times smaller than that of component 3. We evaluated the mean metallicity of the z=3.967 system obtaining values about 0.01 of the solar metallicity or less. However, this should not be taken as representative of the circumburst medium, since the main contribution to the hydrogen column density comes from the outer regions of the galaxy while that of the other elements presumably comes from the ISM closer to the GRB site. Furthermore, difficulties in evaluating dust depletion correction can modify significantly these values. The mean [C/Fe] ratio agrees well with that expected by single star-formation event models. Interestingly the [C/Fe] of component 2 is smaller than that of component 3, in agreement with GRB dust destruction scenarios, if component 2 is closer than component 3 to the GRB site.Comment: 11 pages, 15 postscript figures, accepted for pubblication in A&

The Initial Mass Function in disc galaxies and in galaxy clusters: the chemo-photometric picture

The observed brightness of the Tully-Fisher relation suggests a low stellar M/L ratio and a "bottom-light" IMF in disc galaxies, but the corresponding efficiency of chemical enrichment tends to exceed the observational estimates. Either suitable tuning of the IMF slope and mass limits or metal outflows from disc galaxies must then be invoked. A standard Solar Neighbourhood IMF cannot explain the high metallicity of the hot intra-cluster medium: a different IMF must be at work in clusters of galaxies. Alternatively, if the IMF is universal and chemical enrichment is everywhere as efficient as observed in clusters, substantial loss of metals must occur from the Solar Neighbourhood and from disc galaxies in general; a "non-standard" scenario challenging our understanding of disc galaxy formation.Comment: 6 pages, 4 figures; in Proceedings of IMF@50: the Initial Mass Function 50 years later; Corbelli, Palla and Zinnecker (eds.