On breaking the age-metallicity degeneracy in early-type galaxies: Outflows versus Star Formation Efficiency

A simple model of chemical enrichment in cluster early-type galaxies is presented where the main parameters driving the formation of the stellar component are reduced to four: infall timescale (tf), formation epoch (zF), star formation efficiency (Ceff) and fraction of gas ejected in outflows (Bout). We find that only variations in Bout or Ceff can account for the colour-magnitude relation, so that the most luminous galaxies had low values of ejected gas and high efficiencies. The combination of chemical enrichment tracks with population synthesis models is used to explore the correlation between mass-to-light ratios and masses. A significant slope mismatch is found between stellar and total M/L ratios, which cannot be explained by an age spread and implies a non-linear correlation between total and stellar mass. The sequences driven by star formation efficiency and outflows are shown to predict different trends at high redshift. Measurement of the dependence of the tilt of the fundamental plane on redshift will break the degeneracy between outflows and star formation efficiency, which will enable us to determine whether the colour-magnitude relation is controlled by age or metallicity.Comment: 8 pages, 5 figures. To be published in MNRA

Out-of-plane thermopower of strongly correlated layered systems: an application to Bi_2(Sr,La)_2CaCu_2O_{8+\delta}

We calculate the out-of-plane thermopower in a quasi-two dimensional system, and argue that this quantity is an effective probe of the asymmetry of the single-particle spectral function. We find that the temperature and doping dependence of the out-of-plane thermopower in Bi_2(Sr,La)_2CaCu_2O_{8+\delta} single crystals is broadly consistent with the behavior of the spectral function determined from ARPES and tunneling experiments. We also investigate the relationship between out-of-plane thermopower and entropy in a quasi-two dimensional material. We present experimental evidence that at moderate temperatures, there is a qualitative correspondence between the out-of-plane thermopower in Bi_2(Sr,La)_2CaCu_2O_{8+\delta}, and the entropy obtained from specific heat measurements. Finally, we argue that the derivative of the entropy with respect to particle number may be the more appropriate quantity to compare with the thermopower, rather than the entropy per particle.Comment: 11 pages, 5 figures. v2: substantially rewritten, including a more detailed analysis of the relationship between thermopower and entrop

Type Ia supernovae and the formation history of early-type galaxies

Using the standard prescription for the rates of supernovae type II and type Ia, we compare the predictions of a simple model of star formation in galaxies with the observed radial gradients of abundance ratios in a sample of early-type galaxies to infer the relative contribution of each type of supernova. The data suggests a correlation between the fractional contribution of Type Ia to the chemical enrichment of the stellar populations (1-xi) and central velocity dispersion of order 1-xi ~ -0.16log sigma_0+0.40, so that the type Ia contribution in stars ranges from a negligible amount in massive galaxies up to 10% in low-mass systems. Our model is parametrized by a star formation timescale (t_SF) which controls the duration of the starburst. A correlation with galaxy radius as a power law (t_SF ~ r^beta) translates into a radial gradient of the abundance ratios. The data implies a wide range of formation scenarios for a simple model that fixes the luminosity profile, ranging from inside-out (beta=2), to outside-in formation (beta=-1), as is consistent with numerical simulations of elliptical galaxy formation. An alternative scenario that links t_SF to the dynamical timescale favours inside-out formation over a smaller range. In both cases, massive galaxies are predicted to have undergone a more extended period of star formation in the outer regions with respect to their low-mass counterparts.Comment: Accepted for publication in MNRAS. 8 pages with 5 embedded color EPS figure

Comments on "Limits on Dark Matter Using Ancient Mica"

To appear in Phys. Rev. Lett. together with the author's Reply.Comment: Compressed PostScript (filename.ps.Z), 3 pages, no figure

Solar Seismic Model as a New Constraint on Supersymmetric Dark Matter

If the Milky Way is populated by WIMPs as predicted by cosmological models of the large-scale structure of the universe and as motivated by SUSY, the capture of high-mass WIMPs by the Sun would affect the temperature, density and chemical composition of the solar core. We use the sound speed and the density profiles inferred from the helioseismic instruments on the Solar and Heliospheric Observatory (SOHO) to discuss the effect of WIMP accretion and annihilation on the evolution of the Sun. The WIMP transport of energy inside the Sun is not negligible for WIMPs with a mass smaller than 60 GeV and annihilating WIMPs with ~ 10^{-27}cm^3/sec. WIMP-accreting models with WIMP masses smaller than 30 GeV are in conflict with the most recent seismic data. We combine our new constraints with the analysis of predicted neutrino fluxes from annihilating WIMPs in the solar core. Working in the framework of the Minimal Supersymmetric Standard Model and considering the neutralino as the best dark matter particle candidate, we find that supersymmetric models, consistent with solar seismic data and with recent measurements of dark matter relic density, lead to a measured muon flux on Earth in the range of 1 to 10^4 km^{-2} yr^{-1}, for neutralino masses between 30 and 400 GeV.Comment: Accepeted for publication in MNRA