Cosmological formation and chemical evolution of an elliptical galaxy

We aim at studying the effect of a cosmologically motivated gas infall law for the formation of a massive elliptical galaxy in order to understand its impact on the formation of the spheroids. We replace the empirical infall law of the model by Pipino & Matteucci with a cosmologically derived infall law for the formation of an elliptical galaxy. We constrast our predictions with observations. We also compare the obtained results with those of Pipino & Matteucci. We computed models with and without galactic winds: we found that models without wind predict a too large current SNIa rate. In particular, the cosmological model produces a current SNIa which is about ten times higher than the observed values. Moreover models without wind predict a large current SNII rate, too large even if compared with the recent GALEX data. The predicted SNII rate for the model with wind, on the other hand, is too low if compared with the star formation histories given by GALEX. Last but not least, the mean value for the [Mg/Fe] ratio in the dominant stellar population of the simulated galaxy, as predicted by the cosmological model, is too low if compared to observations. This is, a very important result indicating that the cosmological infall law is in contrast with the chemical evolution. A cosmologically derived infall law for an elliptical galaxy cannot reproduce all the chemical constraints given by the observations. The problem resides in the fact that the cosmologically derived infall law implies a slow gas accretion with consequent star formation rate active for a long period. In this situation low [Mg/Fe] ratios are produced for the dominant stellar population in a typical elliptical, at variance with observations.Comment: 8 pages, 6 figures, accepted for publication by A&

The origin of abundance gradients in the Milky Way: the predictions of different models

We aim at studying the abundance gradients along the Galactic disk and their dependence upon several parameters: a threshold in the surface gas density regulating star formation, the star formation efficiency, the timescale for the formation of the thin disk and the total surface mass density of the stellar halo. We test a model which considers a cosmological infall law. This law does not predict an inside-out disk formation, but it allows to well fit the properties of the solar vicinity. We study several cases. We find that to reproduce at the same time the abundance, star formation rate and surface gas density gradients along the Galactic disk it is necessary to assume an inside-out formation for the disk. The threshold in the gas density is not necessary and the same effect could be reached by assuming a variable star formation efficiency. A cosmologically derived infall law with an inside-out process for the disk formation and a variable star formation efficiency can indeed well reproduce all the properties of the disk. However, the cosmological model presented here does not have sufficient resolution to capture the requested inside-out formation for the disk.Comment: 13 pages, 17 figures and 2 tables. Accepted for publication in Astronomy & Astrophysic

Effects of radial flows on the chemical evolution of the Milky Way disk

The majority of chemical evolution models assume that the Galactic disk forms by means of infall of gas and divide the disk into several independent rings without exchange of matter between them. However, if gas infall is important, radial gas flows should be taken into account as a dynamical consequence of infall. The aim of this paper is to test the effect of radial gas flows on detailed chemical evolution models (one-infall and two-infall) for the Milky Way disk with different prescriptions for the infall law and star formation rate. We found, that with a gas radial inflow of constant speed the metallicity gradient tends to steepen. Taking into account a constant time scale for the infall rate along the Galaxy disk and radial flows with a constant speed, we obtained a too flat gradient, at variance with data, implying that an inside-out formation and/or a variable gas flow speed are required. To reproduce the observed gradients the gas flow should increase in modulus with the galactocentric distance, both in the one-infall and two-infall models. However, the inside-out disk formation coupled with a threshold in the gas density (only in the two-infall model) for star formation and/or a variable efficiency of star formation with galactocentric distance can also reproduce the observed gradients without radial flows. We showed that the radial flows can be the most important process in reproducing abundance gradients but only with a variable gas speed. Finally, one should consider that uncertainties in the data concerning gradients prevent us to draw firm conclusions. Future more detailed data will help to ascertain whether the radial flows are a necessary ingredient in the formation and evolution of the Galactic disk and disks in general.Comment: Accepted by A&A; 11 pages, 16 figure

Open clusters towards the Galactic center: chemistry and dynamics. A VLT spectroscopic study of NGC6192, NGC6404, NGC6583

In the framework of the study of the Galactic metallicity gradient and its time evolution, we present new high-resolution spectroscopic observations obtained with FLAMES and the fiber link to UVES at VLT of three open clusters (OCs) located within $\sim$7~kpc from the Galactic Center (GC): NGC~6192, NGC~6404, NGC~6583. We also present new orbit determination for all OCs with Galactocentric distances (R$_{\rm{GC}}) \leq$8~kpc and metallicity from high-resolution spectroscopy. We aim to investigate the slope of the inner disk metallicity gradient as traced by OCs and at discussing its implication on the chemical evolution of our Galaxy. We have derived memberships of a group of evolved stars for each clusters, obtaining a sample of 4, 4, and 2 member stars in NGC~6192, NGC~6404, and NGC~6583, respectively. Using standard LTE analysis we derived stellar parameters and abundance ratios for the iron-peak elements Fe, Ni, Cr, and for the $\alpha$-elements Al, Mg, Si, Ti, Ca. We calculated the orbits of the OCs currently located within 8~kpc from the GC, and discuss their implication on the present-time radial location. {The average metallicities of the three clusters are all oversolar: [Fe/H]= $+0.12\pm0.04$ (NGC~6192), $+0.11\pm0.04$ (NGC 6404), $+0.37\pm0.03$ (NGC 6583). They are in qualitative agreement with their Galactocentric distances, being all internal OCs, and thus expected to be metal richer than the solar neighborhood. The abundance ratios of the other elements over iron [X/Fe] are consistent with solar values. The clusters we have analysed, together with other OC and Cepheid data, confirm a steep gradient in the inner disk, a signature of an evolutionary rate different than in the outer disk.Comment: 17 pages, 13 figures, A&A accepted for publicatio

The Effect of Different Type Ia Supernova Progenitors on Galactic Chemical Evolution

Our aim is to show how different hypotheses about Type Ia supernova progenitors can affect Galactic chemical evolution. We include different Type Ia SN progenitor models, identified by their distribution of time delays, in a very detailed chemical evolution model for the Milky Way which follows the evolution of several chemical species. We test the single degenerate and the double degenerate models for supernova Ia progenitors, as well as other more empirical models based on differences in the time delay distributions. We find that assuming the single degenerate or the double degenerate scenario produces negligible differences in the predicted [O/Fe] vs. [Fe/H] relation. On the other hand, assuming a percentage of prompt (exploding in the first 100 Myr) Type Ia supernovae of 50%, or that the maximum Type Ia rate is reached after 3-4 Gyr from the beginning of star formation, as suggested by several authors, produces more noticeable effects on the [O/Fe] trend. However, given the spread still existing in the observational data no model can be firmly excluded on the basis of only the [O/Fe] ratios. On the other hand, when the predictions of the different models are compared with the G-dwarf metallicity distribution, the scenarios with very few prompt Type Ia supernovae can be excluded. Models including the single degenerate or double degenerate scenario with a percentage of 10-13% of prompt Type Ia supernovae produce results in very good agreement with the observations. A fraction of prompt Type Ia supernovae larger than 30% worsens the agreement with observations and the same occurs if no prompt Type Ia supernovae are allowed. In particular, two empirical models for the Type Ia SN progenitors can be excluded: the one without prompt Type Ia supernovae and the one assuming delay time distribution going like t^{-0.5}.Comment: Accepted by A&

Chemical gradients in the Milky Way from the RAVE data

Aims. We aim at measuring the chemical gradients of the elements Mg, Al, Si, and Fe along the Galactic radius to provide new constraints on the chemical evolution models of the Galaxy and Galaxy models such as the Besancon model. Thanks to the large number of stars of our RAVE sample we can study how the gradients vary as function of the distance from the Galactic plane. Methods. We analysed three different samples selected from three independent datasets: a sample of 19 962 dwarf stars selected from the RAVE database, a sample of 10 616 dwarf stars selected from the Geneva-Copenhagen Survey (GCS) dataset, and a mock sample (equivalent to the RAVE sample) created by using the GALAXIA code, which is based on the Besancon model. The three samples were analysed by using the very same method for comparison purposes. We integrated the Galactic orbits and obtained the guiding radii (R-g) and the maximum distances from the Galactic plane reached by the stars along their orbits (Z(max)). We measured the chemical gradients as functions of R-g at different Z(max). Results. We found that the chemical gradients of the RAVE and GCS samples are negative and show consistent trends, although they are not equal: at Z(max) < 0.4 kpc and 4.5 < R-g(kpc) < 9.5, the iron gradient for the RAVE sample is d[Fe/H]/dR(g) = -0.065 dex kpc(-1), whereas for the GCS sample it is d[Fe/H]/dR(g) = -0.043 dex kpc(-1) with internal errors of +/-0.002 and +/-0.004 dex kpc(-1), respectively. The gradients of the RAVE and GCS samples become flatter at larger Z(max). Conversely, the mock sample has a positive iron gradient of d[Fe/H]/dR(g) = +0.053 +/- 0.003 dex kpc(-1) at Z(max) < 0.4 kpc and remains positive at any Z(max). These positive and unrealistic values originate from the lack of correlation between metallicity and tangential velocity in the Besancon model. In addition, the low metallicity and asymmetric drift of the thick disc causes a shift of the stars towards lower R-g and metallicity which, together with the thin-disc stars with a higher metallicity and R-g, generates a fictitious positive gradient of the full sample. The flatter gradient at larger Z(max) found in the RAVE and the GCS samples may therefore be due to the superposition of thin-and thick-disc stars, which mimicks a flatter or positive gradient. This does not exclude the possibility that the thick disc has no chemical gradient. The discrepancies between the observational samples and the mock sample can be reduced by i) decreasing the density; ii) decreasing the vertical velocity; and iii) increasing the metallicity of the thick disc in the Besancon model

New analytical solutions for chemical evolution models: : characterizing the population of star-forming and passive galaxies

E. Spitoni, V. Vincenzo, and F. Matteucci, 'New analytical solutions for chemical evolution models: characterizing the population of star-forming and passive galaxies', Astronomy & Astrophysics, Vol 599, first published online 20 February 2017, available at DOI: https://doi.org/10.1051/0004-6361/201629745. Reproduced with permission from Astronomy & Astrophysics, © 2017 ESO.Context. Analytical models of chemical evolution, including inflow and outflow of gas, are important tools for studying how the metal content in galaxies evolves as a function of time. Aims. We present new analytical solutions for the evolution of the gas mass, total mass, and metallicity of a galactic system when a decaying exponential infall rate of gas and galactic winds are assumed. We apply our model to characterize a sample of local star-forming and passive galaxies from the Sloan Digital Sky Survey data, with the aim of reproducing their observed mass-metallicity relation. Methods. We derived how the two populations of star-forming and passive galaxies differ in their particular distribution of ages, formation timescales, infall masses, and mass loading factors. Results. We find that the local passive galaxies are, on average, older and assembled on shorter typical timescales than the local star-forming galaxies; on the other hand, the star-forming galaxies with higher masses generally show older ages and longer typical formation timescales compared than star-forming galaxies with lower masses. The local starforming galaxies experience stronger galactic winds than the passive galaxy population. Exploring the effect of assuming different initial mass functions in our model, we show that to reproduce the observed mass-metallicity relation, stronger winds are requested if the initial mass function is top-heavy. Finally, our analytical models predict the assumed sample of local galaxies to lie on a tight surface in the 3D space defined by stellar metallicity, star formation rate, and stellar mass, in agreement with the well-known fundamental relation from adopting gas-phase metallicity. Conclusions. By using a new analytical model of chemical evolution, we characterize an ensemble of SDSS galaxies in terms of their infall timescales, infall masses, and mass loading factors. Local passive galaxies are, on average, older and assembled on shorter typical timescales than the local star-forming galaxies. Moreover, the local star-forming galaxies show stronger galactic winds than the passive galaxy population. Finally, we find that the fundamental relation between metallicity, mass, and star formation rate for these local galaxies is still valid when adopting the average galaxy stellar metallicity.Peer reviewe

Direct Sensing of Endothelial Oxidants by Vascular Endothelial Growth Factor Receptor-2 and c-Src

BACKGROUND: ADPH oxidase-derived reactive oxygen species (ROS) play important roles in redox homeostasis and signal transduction in endothelial cells (ECs). We previously demonstrated that c-Src plays a key role in VEGF-induced, ROS-dependent selective activation of PI3K-Akt but not PLCγ-1-ERK1/2 signaling pathways. The aim of the present study was to understand how VEGFR-2-c-Src signaling axis 'senses' NADPH oxidase-derived ROS levels and couples VEGF activation of c-Src to the redox state of ECs. METHODOLOGY/PRINCIPAL FINDINGS: Using biotinylated probe that detects oxidation of cysteine thiol (cys-OH) in intracellular proteins, we demonstrate that VEGF induced oxidative modification in c-Src and VEGFR-2, and that reduction in ROS levels using siRNA against p47(phox) subunit of Rac1-dependent NADPH oxidase inhibited this phenomenon. Co-immunoprecipitation studies using human coronary artery ECs (HCAEC) showed that VEGF-induced ROS-dependent interaction between VEGFR-2 and c-Src correlated with their thiol oxidation status. Immunofluorescence studies using antibodies against internalized VEGFR-2 and c-Src demonstrated that VEGF-induced subcellular co-localization of these tyrosine kinases were also dependent on NADPH oxidsase-derived ROS. CONCLUSION/SIGNIFICANCE: These results demonstrate that VEGF induces cysteine oxidation in VEGFR-2 and c-Src in an NADPH oxidase-derived ROS-dependent manner, suggesting that VEGFR-2 and c-Src can 'sense' redox levels in ECs. The data also suggest that thiol oxidation status of VEGFR-2 and c-Src correlates with their ability to physically interact with each other and c-Src activation. Taken together, these findings suggest that prior to activating downstream c-Src-PI3K-Akt signaling pathway, VEGFR-2-c-Src axis requires an NADPH oxidase-derived ROS threshold in ECs

A Stochastic Step Model of Replicative Senescence Explains ROS Production Rate in Ageing Cell Populations

Increases in cellular Reactive Oxygen Species (ROS) concentration with age have been observed repeatedly in mammalian tissues. Concomitant increases in the proportion of replicatively senescent cells in ageing mammalian tissues have also been observed. Populations of mitotic human fibroblasts cultured in vitro, undergoing transition from proliferation competence to replicative senescence are useful models of ageing human tissues. Similar exponential increases in ROS with age have been observed in this model system. Tracking individual cells in dividing populations is difficult, and so the vast majority of observations have been cross-sectional, at the population level, rather than longitudinal observations of individual cells

The cytoprotective drug amifostine modifies both expression and activity of the pro-angiogenic factor VEGF-A

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