New response functions for absorption-line indices from high-resolution spectra

Basing on the huge library of 1-A resolution spectra calculated by Munari et al. over a large range of logT, log g, [Fe/H] and both for solar and a-enhanced abundance ratios [a/Fe], we present theoretical absorption-line indices on the Lick system. First we derive the so-called response functions (RFs) of Tripicco & Bell for a wide range of logT, log g, [Fe/H] and [a/Fe]=+0.4 dex. The RFs are commonly used to correct indices with solar [a/Fe] ratios to indices with [a/Fe]>0. Not only the RFs vary with the type of star but also with the metallicity. Secondly, with the aid of this and the fitting functions (FFs) of Worthey et al., we derive the indices for single stellar populations and compare them with those obtained by previous authors, e.g. Tantalo & Chiosi. The new RFs not only supersede the old ones by Tripicco & Bell, but also show that Hb increases with the degree of enhancement in agreement with the results by Tantalo & Chiosi. The new indices for single stellar populations are used to derive with aid of the recursive Minimum Distance method the age, metallicity and degree of enhancement of a sample of Galactic Globular Clusters for which these key parameters have been independently derived from the Colour-Magnitude Diagram and/or spectroscopic studies. The agreement is remarkably good.Comment: 18 pages, to appear in Astronomy & Astrophysic

Modelling galaxy spectra in presence of interstellar dust. I. The model of ISM and the library of dusty SSPs

In this paper, the first of a series of two devoted to modelling the spectra of galaxies of different morphological type in presence of dust, we present our description of the dust both in the diffuse ISM and the molecular clouds. Our model for the dust takes into account three components, i.e. graphite, silicates and polycyclic aromatic hydrocarbons. We consider and adapt to our aims two prescriptions for the size distribution of the dust grains and two models for the emission of the dusty ISM. We cross-check the emission and extinction models of the ISM by calculating the extinction curves and the emission for the typical environments of the Milky Way and the Large and Small Magellanic Clouds and by comparing the results with the observational data. The final model we have adopted is an hybrid one which stems from combining the analysis of Guhathakurta et al (1989) for the emission of graphite and silicates and Puget et al. (1985) for the PAH emission, and using the distribution law of Weingartner et al. (2001a) and the ionization model for PAHs of Weingartner et al. (2001b). We apply the model to calculate the SED of SSPs of different age and chemical composition, which may be severely affected by dust in young, massive stars while they are still embedded in their parental MCs. We use the "Ray Tracing" method to solve the problem of radiative transfer and to calculate libraries of SSP SEDs. Particular care is paid to model the contribution from PAHs, introducing different abundances of C in the population of very small carbonaceous grains (VSGs) and different ionization states in PAHs. The SEDs of young SSPs are then compared with observational data of star forming regions of four local galaxies successfully reproducing their SEDs from the UV-optical regions to the mid and far infrared.Comment: 24 pages, 29 figure

Spectro-photometric Evolution of Elliptical Galaxies. II. Models with infall

In this paper we present new chemo-spectro-photometric models of elliptical galaxies in which infall of primordial gas is allowed to occur. They aim to simulate the collapse of a galaxy made of two components, i.e. luminous material and dark matter. The mass of the dark component is assumed to be constant in time, whereas that of the luminous material is supposed to accrete at a suitable rate. They also include the effect of galactic winds powered by supernova explosions and stellar winds from massive, early-type stars. The models are constrained to match a number of properties of elliptical galaxies, i.e. the slope and mean colours of the colour-magnitude relation (CMR), V versus (V--K), the UV excess as measured by the colour (1550--V) together with the overall shape of the integrated spectral energy distribution (ISED) in the ultraviolet, the relation between the Mg2 index and (1550--V), the mass to blue luminosity ratio M/Lb as a function of the B luminosity, and finally the broad-band colours (U--B), (B--V), (V--I), (V--K), etc.Comment: pages 22, 20 postscript figures, 2 external table (tab2_infall using supertabular.sty and tab5_infall using supertabular1.sty

Measurements of Far-UV Emission from Elliptical Galaxies at z=0.375

The ``UV upturn'' is a sharp rise in spectra of elliptical galaxies shortward of rest-frame 2500 A. It is a ubiquitous phenomenon in nearby giant elliptical galaxies, and is thought to arise primarily from low-mass evolved stars on the extreme horizontal branch and beyond. Models suggest that the UV upturn is a very strong function of age for these old stellar populations, increasing as the galaxy gets older. In some models the change in UV/optical flux ratio is a factor of 25 over timescales of less than 3 Gyr. To test the predictions for rapid evolution of the UV upturn, we have observed a sample of normal elliptical galaxies in the z=0.375 cluster Abell 370 with the Faint Object Camera aboard the Hubble Space Telescope. A combination of two long-pass filters was used to isolate wavelengths shortward of rest-frame 2700 A, providing a measurement of the UV upturn at a lookback time of approximately 4 Gyr. Surprisingly, the four elliptical galaxies observed show a range of UV upturn strength that is similar to that seen in nearby elliptical galaxies, with an equivalent 1550-V color ranging from 2.9-3.4 mag. Our result is inconsistent with some models for the UV upturn; other models are consistent only for a high redshift of formation (z_f >= 4).Comment: 4 pages, Latex. 1 figure. To appear in ApJL. Uses emulateapj.sty and apjfonts.sty. Revision includes minor ApJ edits & fixes typo

Finite-Volume QED Corrections to Decay Amplitudes in Lattice QCD

We demonstrate that the leading and next-to-leading finite-volume effects in the evaluation of leptonic decay widths of pseudoscalar mesons at $O(\alpha)$ are universal, i.e. they are independent of the structure of the meson. This is analogous to a similar result for the spectrum but with some fundamental differences, most notably the presence of infrared divergences in decay amplitudes. The leading non-universal, structure-dependent terms are of $O(1/L^2)$ (compared to the $O(1/L^3)$ leading non-universal corrections in the spectrum). We calculate the universal finite-volume effects, which requires an extension of previously developed techniques to include a dependence on an external three-momentum (in our case, the momentum of the final state lepton). The result can be included in the strategy proposed in Ref.\,\cite{Carrasco:2015xwa} for using lattice simulations to compute the decay widths at $O(\alpha)$, with the remaining finite-volume effects starting at order $O(1/L^2)$. The methods developed in this paper can be generalised to other decay processes, most notably to semileptonic decays, and hence open the possibility of a new era in precision flavour physics

Electromagnetic corrections to leptonic decay rates of charged pseudoscalar mesons: finite-volume effects

In Carrasco et al. we have recently proposed a method to calculate $O(e^2)$ electromagnetic corrections to leptonic decay widths of pseudoscalar mesons. The method is based on the observation that the infrared divergent contributions (that appear at intermediate stages of the calculation and that cancel in physical quantities thanks to the Bloch-Nordsieck mechanism) are universal, i.e. depend on the charge and the mass of the meson but not on its internal structure. In this talk we perform a detailed analysis of the finite-volume effects associated with our method. In particular we show that also the leading $1/L$ finite-volume effects are universal and perform an analytical calculation of the finite-volume leptonic decay rate for a point-like meson

Leading isospin-breaking corrections to pion, kaon and charmed-meson masses with Twisted-Mass fermions

We present a lattice computation of the isospin-breaking corrections to pseudoscalar meson masses using the gauge configurations produced by the European Twisted Mass collaboration with $N_f = 2 + 1 + 1$ dynamical quarks at three values of the lattice spacing ($a \simeq 0.062, 0.082$ and $0.089$ fm) with pion masses in the range $M_\pi \simeq 210 - 450$ MeV. The strange and charm quark masses are tuned at their physical values. We adopt the RM123 method based on the combined expansion of the path integral in powers of the $d$- and $u$-quark mass difference ($\widehat{m}_d - \widehat{m}_u$) and of the electromagnetic coupling $\alpha_{em}$. Within the quenched QED approximation, which neglects the effects of the sea-quark charges, and after the extrapolations to the physical pion mass and to the continuum and infinite volume limits, we provide results for the pion, kaon and (for the first time) charmed-meson mass splittings, for the prescription-dependent parameters $\epsilon_{\pi^0}$, \epsilon_\gamma(\overline{MS}, 2~\mbox{GeV}), \epsilon_{K^0}(\overline{MS}, 2~\mbox{GeV}), related to the violations of the Dashen's theorem, and for the light quark mass difference (\widehat{m}_d - \widehat{m}_u)(\overline{MS}, 2~\mbox{GeV}).Comment: 47 pages, 20 figures, 4 tables; comments on QED and QCD splitting prescriptions added; version to appear in PR