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Ignacio Ferreras Alessandro Melchiorri Domenico Tocchini-Valentini 《Monthly notices of the Royal Astronomical Society》2003,344(1):257-261
The age of the Universe has been increasingly constrained by different techniques, such as the observations of type Ia supernovae (SNIa) at high redshift or dating the stellar populations of globular clusters. In this paper, we present a complementary approach using the colours of the brightest elliptical galaxies in clusters over a wide redshift range ( z ≲ 1) . We put new and independent bounds on the dark energy equation of state parametrized by a constant pressure-to-density ratio w Q and by a parameter (ξ) which determines the scaling between the matter and dark energy densities. We find that accurate estimates of the metallicities of the stellar populations in moderate and high-redshift cluster galaxies can pose stringent constraints on the parameters that describe dark energy. Our results are in good agreement with the analysis of dark energy models using SNIa data as a constraint. Accurate estimates of the metallicities of stellar populations in cluster galaxies at z ≲ 2 will make this approach a powerful complement to studies of cosmological parameters using high-redshift SNIa. 相似文献
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Using a set of compilations of measurements for extragalactic radio sources, we construct all-sky maps of the Faraday rotation produced by the Galactic magnetic field. In order to generate the maps, we treat the radio source positions as a kind of 'mask' and construct combinations of spherical harmonic modes that are orthogonal on the masked sky. As long as relatively small multipoles are used, the resulting maps are quite stable to changes in the selection criteria for the sources, and show clearly the structure of the local Galactic magnetic field. We also suggest the use of these maps as templates for cosmic microwave background (CMB) foreground analysis, illustrating the idea with a cross-correlation analysis between the Wilkinson Microwave Anisotropy Probe ( WMAP ) data and our maps. We find a significant cross-correlation, indicating the presence of a significant residual contamination. 相似文献
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The Cambrian-Vendian groundwater body plays an important role in drinking water supply of capital Tallinn and other settlements
in northern Estonia. Water quality in this deep-seated confined groundwater body is influenced by the intrusion of present-day
seawater and pumping-induced upward migration of deeper saline groundwater. The aim of this study is to evaluate the threshold
values applying the methodology worked out within the EU 6th FP project “Background criteria for the identification of groundwater
thresholds (BRIDGE)” and to compare the results with the values proposed by local authorities. A database containing 250 monitoring
points was completed and used for the calculation of natural background levels (as the 90 and 97.7 percentile) in groundwater.
The calculation of threshold values is based on natural background levels and reference values. In case of Cambrian-Vendian
groundwater body the receptor is drinking water, thus limit values set by Estonian drinking water standard were used as reference
values. The threshold values proposed by local authorities are more or less the same as calculated by BRIDGE methodology.
Exceptionally different values are derived in case of chloride and ammonium. 相似文献