Rates and properties of type Ia supernovae as a function of mass and star-formation in their host galaxies

(ABRIDGED) We show that Type Ia supernovae (SNe Ia) are formed within both very young and old stellar populations, with observed rates that depend on the stellar mass and mean star-formation rates (SFRs) of their host galaxies. Models where the SN Ia rate depends solely on host galaxy stellar mass are ruled out with 99% confidence. Our analysis is based on 100 spectroscopically-confirmed SNe Ia, plus 24 photometrically-classified events, all from the Supernova Legacy Survey (SNLS) and distributed over 0.2<z<0.75. Using multi-band photometry, we estimate stellar masses and SFRs for the SN Ia host galaxies by fitting their broad-band spectral energy distributions with the galaxy spectral synthesis code, PEGASE.2. We show that the SN Ia rate per unit mass is proportional to the specific SFR of the parent galaxies -- more vigorously star-forming galaxies host more SNe Ia per unit stellar mass, broadly equivalent to the trend of increasing SN Ia rate in later-type galaxies seen in the local universe. Following earlier suggestions for a simple "two-component" model approximating the SN Ia rate, we find bivariate linear dependencies of the SN Ia rate on both the stellar masses and the mean SFRs of the host systems. We also demonstrate a dependence of distant SN Ia light-curve shapes on star-formation in the host galaxy, similar to trends observed locally. Passive galaxies, with no star-formation, preferentially host faster-declining/dimmer SNe Ia, while slower-declining/brighter events are only found in systems with ongoing star-formation. We model the light-curve width distribution in star-forming galaxies as the sum of a young component, and an old component taken from the distribution in non-star-forming galaxies.Comment: Accepted for publication in Ap

DEMON: a proposal for a satellite-borne experiment to study dark matter and dark energy

We outline a novel satellite mission concept, DEMON, aimed at advancing our comprehension of both dark matter and dark energy, taking full advantage of two complementary methods: weak lensing and the statistics of galaxy clusters. We intend to carry out a 5000 deg2 combined IR, optical and X-ray survey with galaxies up to a redshift of z~2 in order todetermine the shear correlation function. We will also find ~100000 galaxy clusters, making it the largest survey of this type to date. The DEMON spacecraft will comprise one IR/optical and eight X-ray telescopes,coupled to multiple cameras operating at different frequency bands. To a great extent, the technology employed has already been partially tested on ongoing missions, therefore ensuring improved reliability

Œuvrer pour le salut

Le problème du salut personnel et collectif, crucial pour tous les chrétiens, entraîne l’émergence d’individus et de groupes sociaux réputés particulièrement aptes à faire leur propre salut et à œuvrer pour celui des autres. Partant de cette donnée fondamentale, le présent ouvrage examine la tension entre les ambitions spirituelles et les contraintes individuelles, communautaires et institutionnelles des moines, des chanoines réguliers et des frères mendiants, dans le cadre du Moyen Âge hispanique. Trois modalités d’accès au salut sont mises en évidence : la conversion, c’est-à-dire le choix d’entrer en religion et la continuelle transformation individuelle qu’il suppose ; la médiation, fondée sur la prière et sur la liturgie ; le soin des âmes enfin, lié à l’engagement pastoral.El problema de la salvación personal y colectiva, crucial para todos los cristianos, lleva a la aparición de individuos y grupos sociales considerados particularmente capaces de salvarse a sí mismos y de trabajar por la salvación de los demás. Partiendo de este hecho, este libro examina la tensión entre las ambiciones espirituales y las limitaciones individuales, comunitarias e institucionales de los monjes, canónigos regulares y frailes mendicantes en el contexto de la Edad Media hispana