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Constraints on the redshift dependence of the dark energy potential
We develop a formalism to characterize the shape and the redshift evolution of the dark energy potential. Our formalism makes use of quantities similar to the horizon-flow parameters in inflation andExpand
A 3.5-Gyr-old galaxy at redshift 1.55
ONE of the most direct methods of constraining the epoch at which the first galaxies formed—and thereby to constrain the age of the Universe—is to identify and date the oldest galaxies at highExpand
LBDS 53W091: An Old, Red Galaxy at z = 1.552*
The weak radio source LBDS 53W091 is associated with a very faint (R ? 24.5) red (R - K ? 5.8) galaxy. Long spectroscopic integrations with the W. M. Keck telescope have provided an absorption-lineExpand
Cosmic chronometers: constraining the equation of state of dark energy. I: H(z) measurements
We present new determinations of the cosmic expansion history from red-envelope galaxies. We have obtained for this purpose high-quality spectra with the Keck-LRIS spectrograph of red-envelopeExpand
The star-formation history of the Universe from the stellar populations of nearby galaxies
An analysis of the ‘fossil record’ of the current stellar populations of 96,545 nearby galaxies, from which a complete star-formation history is obtained, which broadly support those derived from high-redshift galaxies and shows that the peak of star formation was more recent. Expand
Improved constraints on the expansion rate of the Universe up to z ∼ 1.1 from the spectroscopic evolution of cosmic chronometers
We present new improved constraints on the Hubble parameter H(z) in the redshift range 0.15 \textless z \textless 1.1, obtained from the differential spectroscopic evolution of early-type galaxies asExpand
The cosmic evolution of metallicity from the SDSS fossil record
We infer the time evolution of the stellar metallicity for Sloan Digital Sky Survey (SDSS) galaxies by interpreting their spectra through stellar population models using a sample that spans 5 ordersExpand
The star formation histories of galaxies in the sloan digital sky survey
We present the results of a MOPED analysis of ∼3 × 10 5 galaxy spectra from the Sloan Digital Sky Survey Data Release 3 (SDSS DR3), with a number of improvements in data, modelling and analysisExpand
The Cosmic Production of Helium
This work estimates the cosmic production rate of helium relative to metals using K dwarf stars in the Hipparcos catalog with accurate spectroscopic metallicities using ΔY/ΔZ = 2.1 ± 0.4 at the 68% confidence level. Expand
A 6% measurement of the Hubble parameter at z∼0.45: direct evidence of the epoch of cosmic re-acceleration
Deriving the expansion history of the Universe is a major goal of modern cosmology. To date, the most accurate measurements have been obtained with Type Ia Supernovae (SNe) and Baryon AcousticExpand