No abstract

The Sloan Digital Sky Survey (SDSS) started a new phase in 2008 August, with new instrumentation and new surveys focused on Galactic structure and chemical evolution, measurements of the baryon oscillation feature in the clustering of galaxies and the quasar Lyα forest, and a radial velocity search for planets around ∼8000 stars. This paper describes the first data release of SDSS-III (and the eighth counting from the beginning of the SDSS). The release includes five-band imaging of roughly 5200 deg 2 in the southern Galactic cap, bringing the total footprint of the SDSS imaging to 14,555 deg 2 , or over a third of the Celestial Sphere. All the imaging data have been reprocessed with an improved sky-subtraction algorithm and a final, self-consistent photometric recalibration and flat-field determination. This release also includes all data from the second phase of the Sloan Extension for Galactic Understanding and Exploration (SEGUE-2), consisting of spectroscopy of approximately 118,000 stars at both high and low Galactic latitudes. All the more than half a million stellar spectra obtained with the SDSS spectrograph have been reprocessed through an improved stellar parameter pipeline, which has better determination of metallicity for high-metallicity stars.

Using data from the COSMOS survey, we perform the first joint analysis of galaxy-galaxy weak lensing, galaxy spatial clustering, and galaxy number densities. Carefully accounting for sample variance and for scatter between stellar and halo mass, we model all three observables simultaneously using a novel and self-consistent theoretical framework. Our results provide strong constraints on the shape and redshift evolution of the stellar-to-halo mass relation (SHMR) from z = 0.2 to z = 1. At low stellar mass, we find that halo mass scales as M h ∝ M 0.46 * and that this scaling does not evolve significantly with redshift from z = 0.2 to z = 1. The slope of the SHMR rises sharply at M * > 5 × 10 10 M ⊙ and as a consequence, the stellar mass of a central galaxy becomes a poor tracer of its parent halo mass. We show that the dark-to-stellar ratio, M h /M * , varies from low to high masses, reaching a minimum of M h /M * ∼ 27 at M * = 4.5 × 10 10 M ⊙ and M h = 1.2 × 10 12 M ⊙ . This minimum is important for models of galaxy formation because it marks the mass at which the accumulated stellar growth of the central galaxy has been the most efficient. We describe the SHMR at this minimum in terms of the "pivot stellar mass", M piv * , the "pivot halo mass", M piv h , and the "pivot ratio", (M h /M * ) piv . Thanks to a homogeneous analysis of a single data set spanning a large redshift range, we report the first detection of mass downsizing trends for both M piv h and M piv * . The pivot stellar mass decreases from M piv * = 5.75±0.13×10 10 M ⊙ at z = 0.88 to M piv * = 3.55±0.17×10 10 M ⊙ at z = 0.37. Intriguingly, however, the corresponding evolution of M piv h leaves the pivot ratio constant with redshift at (M h /M * ) piv ∼ 27. We use simple arguments to show how this result raises the possibility that star formation quenching may ultimately depend on M h /M * and not simply M h , as is commonly assumed. We show that simple models with such a dependence naturally lead to downsizing in the sites of star formation. Finally, we discuss the implications of our results in the context of popular quenching models, including disk instabilities and AGN feedback.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

We show that the assumption of a flat universe induces critically large errors in reconstructing the dark energy equation of state at z 0.9 even if the true cosmic curvature is very small, O(1%) or less. The spuriously reconstructed w(z) shows a range of unusual behaviour, including crossing of the phantom divide and mimicking of standard tracking quintessence models. For 1% curvature and ΛCDM, the error in w grows rapidly above z ∼ 0.9 reaching (50%, 100%) by redshifts of (2.5, 2.9) respectively, due to the long cosmological lever arm. Interestingly, the w(z) reconstructed from distance data and Hubble rate measurements have opposite trends due to the asymmetric influence of the curved geodesics. These results show that including curvature as a free parameter is imperative in any future analyses attempting to pin down the dynamics of dark energy, especially at moderate or high redshifts.Introduction The quest to distinguish between a cosmological constant, dynamical dark energy and modified gravity has become the dominant obsession in cosmology. Formally elevated to the status of one of the most important problems in fundamental physics, [22] [23] uncovering the true nature of dark energy, as encapsulated in the ratio of its pressure to density, w(z) = p DE /ρ DE , has become the focus of multi-billion dollar proposed experiments using a wide variety of methods, many at redshifts above unity (see e.g. [1]).Unfortunately these experiments will only measure a meagre number of w(z) parameters to any precisionperhaps two or three [3] [24] -since the standard methods all involve integrals over w(z) and typically suffer from subtle systematic effects. As a result of this information limit, studies of dark energy have traditionally fallen into two groups. The first group (see e.g. [10]) have taken their parameters to include (Ω m , Ω DE , w) with w constant and often set to −1. The 2nd group are interested in dynamical dark energy and have typically assumed Ω k = 0 for simplicity while concentrating on constraining w(z) parameters (see e.g. [11] ) [25].In retrospect, the origins of the common practise of ignoring curvature in studies of dynamical dark energy are clear. Firstly, the curved geodesics add an unwelcome complexity to the analysis that has typically been ignored in favour of studies of different parametrisations of w(z). Secondly, standard analysis of the Cosmic Microwave Background (CMB) and Baryon Acoustic Oscillations (BAO) in the context of adiabatic ΛCDM also put stringent limits on the curvature parameter, e.g. Ω k = −0.003 ± 0.010 from WMAP + SDSS [12,13]. As a result it was taken for granted that the impact on the reconstructed w(z) would then be proportional to Ω k and hence small compared to experimental errors.Further support for the view that Ω k should not be included in studies of dark energy came from informa-