Galactic and Cosmic Type Ia SN rates: is it possible to impose constraints on SNIa progenitors?

We compute the Type Ia supernova rates in typical elliptical galaxies by varying the progenitor models for Type Ia supernovae. To do that a formalism which takes into account the delay distribution function (DTD) of the explosion times and a given star formation history is adopted. Then the chemical evolution for ellipticals with baryonic initial masses $10^{10}$, $10^{11}$ and $10^{12} M_{\odot}$ is computed, and the mass of Fe produced by each galaxy is precisely estimated. We also compute the expected Fe mass ejected by ellipticals in typical galaxy clusters (e.g. Coma and Virgo), under different assumptions about Type Ia SN progenitors. As a last step, we compute the cosmic Type Ia SN rate in an unitary volume of the Universe by adopting several cosmic star formation rates and compare it with the available and recent observational data. Unfortunately, no firm conclusions can be derived only from the cosmic SNIa rate, neither on SNIa progenitors nor on the cosmic star formation rate. Finally, by analysing all our results together, and by taking into account previous chemical evolution results, we try to constrain the best Type Ia progenitor model. We conclude that the best progenitor models for Type Ia SNe are still the single degenerate model, the double degenerate wide model, and the empirical bimodal model. All these models require the existence of prompt Type Ia supernovae, exploding in the first 100 Myr since the beginning of star formation, although their fraction should not exceed 15-20% in order to fit chemical abundances in galaxies.Comment: 17 pages, 11 figures, Submitted to MNRA

The properties of Brightest Cluster Galaxies in the SDSS DR6 adaptive matched filter cluster catalogue

We study the properties of Brightest Cluster Galaxies (BCGs) drawn from a catalogue of more than 69000 clusters in the SDSS DR6 based on the adaptive matched filter technique (AMF, Szabo et al., 2010). Our sample consists of more than 14300 galaxies in the redshift range 0.1-0.3. We test the catalog by showing that it includes well-known BCGs which lie in the SDSS footprint. We characterize the BCGs in terms of r-band luminosities and optical colours as well as their trends with redshift. In particular, we define and study the fraction of blue BCGs, namely those that are likely to be missed by either colour-based cluster surveys and catalogues. Richer clusters tend to have brighter BCGs, however less dominant than in poorer systems. 4-9% of our BCGs are at least 0.3 mag bluer in the g-r colour than the red-sequence at their given redshift. Such a fraction decreases to 1-6% for clusters above a richness of 50, where 3% of the BCGs are 0.5 mag below the red-sequence. A preliminary morphological study suggests that the increase in the blue fraction at lower richnesses may have a non-negligible contribution from spiral galaxies. We show that a colour selection based on the g-r red-sequence or on a cut at colour u-r >2.2 can lead to missing the majority of such blue BCGs. We also extend the colour analysis to the UV range by cross-matching our catalogue with publicly available data from Galex GR4 and GR5. We show a clear correlation between offset from the optical red-sequence and the amount of UV-excess. Finally, we cross-matched our catalogue with the ACCEPT cluster sample (Cavagnolo et al., 2009), and find that blue BCGs tend to be in clusters with low entropy and short cooling times. That is, the blue light is presumably due to recent star formation associated to gas feeding by cooling flows. (abridged)Comment: 15 pages, 15 figures, submitted to MNRA

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 properties of brightest cluster galaxies in the Sloan Digital Sky Survey Data Release 6 adaptive matched filter cluster catalogue

We study the properties of brightest cluster galaxies (BCGs) drawn from a catalogue of more than 69 000 clusters in the Sloan Digital Sky Survey (SDSS) Data Release 6 based on the adaptive matched filter technique. Our sample consists of more than 14 300 galaxies in the redshift range 0.1-0.3. We test the catalogue by showing that it includes well-known BCGs which lie in the SDSS footprint. We characterize the Szabo et al. catalogue content in terms of BCGs r-band luminosities and optical colours as well as their trends with redshift. We find that the BCG luminosity distribution is close to a Gaussian with mean −22 mag and dispersion 0.54 mag. The mean has a redshift evolution broadly consistent with pure aging of the galaxies. Richer clusters tend to have brighter BCGs (mean −22.5 mag), however less dominant than in poorer systems. In particular, we define and study the fraction of blue BCGs, namely those that are likely to be missed by either colour-based cluster surveys and catalogues, as shown by a direct comparison to maxBCG clusters that are matched in the Szabo et al. catalogue. The overall fraction of blue BCGs goes from ∼5 per cent in the redshift range 0.1-0.2 to ∼10 per cent in the redshift bin 0.2-0.3, with the average over the whole sample of ∼8 per cent. We estimate the possible contamination due to blue outliers at the 1-2 per cent level, while errors on the photometric redshift may lead to an erroneous classification of >0.5 per cent of actual red BCGs as blue. When considering only galaxies with spectroscopic redshift available and for clusters above a richness of 50 - where the catalogue is more than 85 per cent complete - our conservative estimate of the blue fraction is 1-6 per cent (at 99.6 per cent confidence). A preliminary morphological study suggests that the increase in the blue fraction at lower richnesses may have a non-negligible contribution from spiral galaxies. Finally, we cross-matched our catalogue with the ACCEPT cluster sample, and find that blue BCGs tend to be in clusters with low entropy and short cooling times. That is, the blue light is presumably due to recent star formation associated to gas feeding by cooling flow

An Optical Catalog of Galaxy Clusters Obtained from an Adaptive Matched Filter Finder Applied to SDSS DR6

We present a new cluster catalog extracted from the Sloan Digital Sky Survey Data Release 6 (SDSS DR6) using an adaptive matched filter (AMF) cluster finder. We identify 69,173 galaxy clusters in the redshift range 0.045 $\le z <$ 0.78 in 8420 sq. deg. of the sky. We provide angular position, redshift, richness, core and virial radii estimates for these clusters, as well as an error analysis for each of these quantities. We also provide a catalog of more than 205,000 galaxies representing the three brightest galaxies in the $r$ band which are possible BCG candidates. We show basic properties of the BCG candidates and study how their luminosity scales in redshift and cluster richness. We compare our catalog with the maxBCG and GMBCG catalogs, as well as with that of Wen, Han, and Liu. We match between 30% and 50% of clusters between catalogs over all overlapping redshift ranges. We find that the percentage of matches increases with the richness for all catalogs. We cross match the AMF catalog with available X-ray data in the same area of the sky and find 539 matches, 119 of which with temperature measurements. We present scaling relations between optical and X-ray properties and cluster center comparison. We find that both $\Lambda_{200}$ and $R_{200}$ correlate well with both $L_X$ and $T_X$, with no significant difference in trend if we restrict the matches to flux-limited X-ray samples.Comment: 59 pages, 28 figures; accepted for publication in The Astrophysical Journa

GalICS II: the [alpha/Fe]-mass relation in elliptical galaxies

We aim at reproducing the mass- and sigma-[alpha/Fe] relations in the stellar populations of early-type galaxies by means of a cosmologically motivated assembly history for the spheroids. We implement a detailed treatment for the chemical evolution of H, He, O and Fe in GalICS, a semi-analytical model for galaxy formation which successfully reproduces basic low- and high-redshift galaxy properties. The contribution of supernovae (both type Ia and II) as well as low- and intermediate-mass stars to chemical feedback are taken into account. We find that this chemically improved GalICS does not produce the observed mass- and sigma-[alpha/Fe] relations. The slope is too shallow and scatter too large, in particular in the low and intermediate mass range. The model shows significant improvement at the highest masses and velocity dispersions, where the predicted [alpha/Fe] ratios are now marginally consistent with observed values. We show that this result comes from the implementation of AGN (plus halo) quenching of the star formation in massive haloes. A thorough exploration of the parameter space shows that the failure of reproducing the mass- and sigma-[alpha/Fe] relations can partly be attributed to the way in which star formation and feedback are currently modelled. The merger process is responsible for a part of the scatter. We suggest that the next generation of semi-analytical model should feature feedback (either stellar of from AGN) mechanisms linked to single galaxies and not only to the halo, especially in the low and intermediate mass range. The integral star formation history of a single galaxy determines its final stellar [alpha/Fe] as it might be expected from the results of closed box chemical evolution models. (abridged)Comment: 12 pages, 13 figure, A&A submitted, comments welcom

Fertility and survival of Swedish Red and White × Holstein crossbred cows and purebred Holstein cows

Swedish Red and White × Holstein (S×H) cows were compared with pure Holstein (HOL) cows for fertility and survival traits in 2 commercial dairy farms in central-southern Córdoba province, Argentina, over 6 years (2008–2013). The following traits were evaluated: first service conception rate (FSCR), overall conception rate (CR), number of services per conception (SC), days open (DO), mortality rate, culling rate, survival to subsequent calvings, and length of productive life (LPL). The data set consisted of 506 lactations from 240 S×H crossbred cows and 1,331 lactations from 576 HOL cows. The FSCR and CR were analyzed using logistic regression, DO and LPL were analyzed using a Cox's proportional hazards regression model, and differences of proportions were calculated for mortality rate, culling rate, and survival to subsequent calvings. The S×H cows were superior to HOL cows in overall lactations for all the fertility traits (+10.5% FSCR, +7.7% CR, −0.5 SC, and 35 fewer DO). During the first lactation, S×H cows were superior to HOL cows for all fertility traits (+12.8% FSCR, +8.0% CR, −0.4 SC, and 34 fewer DO). In the second lactation, S×H cows exhibited lower SC (−0.5) and 21 fewer DO than HOL cows. In the third or greater lactations, S×H cows showed higher FSCR (+11.0%) and CR (+12.2%), lower SC (−0.8), and 44 fewer DO than pure HOL cows. In addition, S×H cows had a lower mortality rate (−4.7%) and a lower culling rate (−13.7%) than HOL cows. Due to the higher fertility and lower mortality and culling rates, the S×H cows had higher survival to the second (+9.2%), third (+16.9%), and fourth (+18.7%) calvings than HOL cows. Because of these results, S×H cows had longer LPL (+10.3 mo) than HOL cows. These results indicate that S×H cows had higher fertility and survival than HOL cows on commercial dairy farms in Argentina.Fil: Pipino, D. F.. Universidad Nacional de Río Cuarto. Facultad de Agronomía y Veterinaria. Departamento de Producción Animal; ArgentinaFil: Piccardi, Mónica Belén. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigaciones Agropecuarias. Unidad de Fitopatología y Modelización Agrícola - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Unidad de Fitopatología y Modelización Agrícola; ArgentinaFil: Lopez Villalobos, Nicolas. Massey University; Nueva ZelandaFil: Hickson, R. E.. Massey University; Nueva ZelandaFil: Vazquez, Maria Isabel. Universidad Nacional de Río Cuarto. Facultad de Agronomía y Veterinaria. Departamento de Producción Animal; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentin

Is the metallicity of their hosts a good measure of the metallicity of Type Ia supernovae?

The efficient use of Type Ia supernovae (SNIa) for cosmological studies requires knowledge of any parameter that can affect their luminosity in either systematic or statistical ways. Observational samples of SNIa commonly use the metallicity of the host galaxy, Z_host, as an estimator of the supernova progenitor metallicity, Z_Ia, that is one of the primary factors affecting SNIa magnitude. Here, we present a theoretical study of the relationship between Z_Ia and Z_host. We follow the chemical evolution of homogeneous galaxy models together with the evolution of the supernova rates in order to evaluate the metallicity distribution function, MDF(Delta Z), i.e. the probability that the logarithm of the metallicity of a SNIa exploding now differs in less than Delta Z from that of its host. We analyse several model galaxies aimed to represent from active to passive galaxies, including dwarf galaxies prone to experience supernova driven outflows. We analyse the sensitivity of the MDF to uncertain ingredients: IMF, star-formation law, stellar lifetime, stellar yields, and SNIa delay-time distribution. There is a remarkable degree of agreement between the mean Z_Ia in a galaxy and its Z_host when they both are measured as the CNO abundance, especially if the DTD peaks at small time delays, while the average Fe abundance of host and SNIa may differ up to 0.4-0.6 dex in passive galaxies. The dispersion of Z_Ia in active galaxy models is quite small, meaning that Z_host is a quite good estimator of the supernova metallicity. Passive galaxies present a larger dispersion, which is more pronounced in low mass galaxies. We discuss the use of different metallicity indicators: Fe vs. O, and gas-phase metallicity vs. stellar metallicity. The results of the application of our formalism to a galactic catalogue (VESPA) are roughly consistent with our theoretical estimates. (abridged)Comment: 15 pages, 10 figures, 1 table, accepted for MNRA

The Origin and Evolution of the Mass-Metallicity Relation using GalICS

The GalICS (Galaxies in Cosmological Simulations) semi-analytical model of hierar- chical galaxy formation is used to investigate the effects of different galactic properties, including star formation rate (SFR) and outflows, on the shape of the mass metallic- ity relation and to predict the relation for galaxies at redshift z=2.27 and z=3.54. Our version of GalICS has the chemical evolution implemented in great detail and is less heavily reliant on approximations such as instantaneous recycling. We vary the model parameters controlling both the efficiency and redshift dependence of the SFR as well as the efficiency of supernova feedback. We find that the factors controlling the SFR influence the relation significantly at all redshifts and require a strong redshift dependence, proportional to 1+z, in order to reproduce the observed relation at the low mass end. Indeed, at any redshift, the predicted relation flattens out at the high mass end resulting in a poorer agreement with observations in this regime. We also find that variation of the parameters associated with outflows has a minimal effect on the relation at high redshift but does serve to alter its shape in the more recent past. We thus conclude that the relation is one between SFR and mass and that outflows are only important in shaping the relation at late times. When the relation is stratified by SFR it is apparent that the predicted galaxies with increasing stellar masses have higher SFRs, supporting the view that galaxy downsizing is the origin of the relation. Attempting to reproduce the observed relation, we vary the parameters controlling the efficiency of star formation and its redshift dependence and compare the predicted relations with Erb et al. (2006) at z=2.27 and Maiolino et al. (2008) at z=3.54 in order to find the best-fitting parameters. (Abridged)Comment: 16 pages, 9 figures, 1 table, accepted for publication in MNRA