113 research outputs found
A Robust Distance Measurement and Dark Energy Constraints from the Spherically-Averaged Correlation Function of Sloan Digital Sky Survey Luminous Red Galaxies
We measure the effective distance to z=0.35, D_V(0.35), from the overall
shape of the spherically-averaged two-point correlation function of the Sloan
Digital Sky Survey (SDSS) Data Release 7 (DR7) luminous red galaxy (LRG)
sample. We find D_V(0.35)=1428_{-73}^{+74} without assuming a dark energy model
or a flat Universe. We find that the derived measurement of
r_s(z_d)/D_V(0.35)=0.1143 \pm 0.0030 (the ratio of the sound horizon at the
drag epoch to the effective distance to z=0.35) is more tightly constrained and
more robust with respect to possible systematic effects. It is also nearly
uncorrelated with \Omega_m h^2.
Combining our results with the cosmic microwave background and supernova
data, we obtain \Omega_k=-0.0032^{+0.0074}_{-0.0072} and
w=-1.010^{+0.046}_{-0.045} (assuming a constant dark energy equation of state).
By scaling the spherically-averaged correlation function, we find the Hubble
parameter H(0.35)=83^{+13}_{-15} km s^{-1}Mpc^{-1} and the angular diameter
distance D_A(0.35)=1089^{+93}_{-87} Mpc.
We use LasDamas SDSS mock catalogs to compute the covariance matrix of the
correlation function, and investigate the use of lognormal catalogs as an
alternative. We find that the input correlation function can be accurately
recovered from lognormal catalogs, although they give larger errors on all
scales (especially on small scales) compared to the mock catalogs derived from
cosmological N-body simulations.Comment: revised, 12 pages, 12 figure
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A critical knowledge pathway to low-carbon, sustainable futures: Integrated understanding of urbanization, urban areas, and carbon
Clustering of Luminous Red Galaxies IV: Baryon Acoustic Peak in the Line-of-Sight Direction and a Direct Measurement of H(z)
We study the clustering of LRG galaxies in the latest spectroscopic SDSS data
releases, DR6 and DR7, which sample over 1 Gpc^3/h^3 to z=0.47. The 2-point
correlation function \xisp is estimated as a function of perpendicular
and line-of-sight (radial) directions. We find a significant
detection of a peak at Mpc/h, which shows as a circular ring in
the plane. There is also significant evidence for a peak along the
radial direction whose shape is consistent with its originating from the
recombination-epoch baryon acoustic oscillations (BAO). A \xisp model with no
radial BAO peak is disfavored at , whereas a model with no
magnification bias is disfavored at . The radial data enable, for the
first time, a direct measurement of the Hubble parameter as a function
of redshift. This is independent from earlier BAO measurements which used the
spherically averaged (monopole) correlation to constrain an integral of .
Using the BAO peak position as a standard ruler in the radial direction, we
find: km/s/Mpc for z=0.15-0.30 and
km/s/Mpc for . The first
error is a model independent statistical estimation and the second accounts for
systematics both in the measurements and in the model. For the full sample,
, we find km/s/Mpc.Comment: Minor revision to match version accepted for publication in MNRAS.
Includes comparison to DR7, a Table with the measurements and errors.
Includes extended analysis on systematic errors. Some figures have been
omitted. Main results and conclusions remain unchange
Interpreting large-scale redshift-space distortion measurements
The simplest theory describing large-scale redshift-space distortions (RSD),
based on linear theory and distant galaxies, depends on the growth of
cosmological structure, suggesting that strong tests of General Relativity can
be constructed from galaxy surveys. As data sets become larger and the expected
constraints more precise, the extent to which the RSD follow the simple theory
needs to be assessed in order that we do not introduce systematic errors into
the tests by introducing inaccurate simplifying assumptions. We study the
impact of the sample geometry, non-linear processes, and biases induced by our
lack of understanding of the radial galaxy distribution on RSD measurements.
Using LasDamas simulations of the Sloan Digital Sky Survey II (SDSS-II)
Luminous Red Galaxy (LRG) data, these effects are shown to be important at the
level of 20 per cent. Including them, we can accurately model the recovered
clustering in these mock catalogues on scales 30 -- 200 Mpc/h. Applying this
analysis to robustly measure parameters describing the growth history of the
Universe from the SDSS-II data, gives
and
when no prior is imposed on the
growth-rate, and the background geometry is assumed to follow a CDM
model with the WMAP + SNIa priors. The standard WMAP constrained CDM
model with General Relativity predicts
and
, which is fully consistent with
these measurements.Comment: 20 pages, 17 figures, 1 tabl
Measuring D_A and H at z=0.35 from the SDSS DR7 LRGs using baryon acoustic oscillations
We present measurements of the angular diameter distance D_A(z) and the
Hubble parameter H(z) at z=0.35 using the anisotropy of the baryon acoustic
oscillation (BAO) signal measured in the galaxy clustering distribution of the
Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) Luminous Red Galaxies
(LRG) sample. Our work is the first to apply density-field reconstruction to an
anisotropic analysis of the acoustic peak. Reconstruction partially removes the
effects of non-linear evolution and redshift-space distortions in order to
sharpen the acoustic signal. We present the theoretical framework behind the
anisotropic BAO signal and give a detailed account of the fitting model we use
to extract this signal from the data. Our method focuses only on the acoustic
peak anisotropy, rather than the more model-dependent anisotropic information
from the broadband power. We test the robustness of our analysis methods on 160
LasDamas DR7 mock catalogues and find that our models are unbiased at the ~0.2%
level in measuring the BAO anisotropy. After reconstruction we measure
D_A(z=0.35)=1050+/-38 Mpc and H(z=0.35)=84.4+/-7.0 km/s/Mpc assuming a sound
horizon of r_s=152.76 Mpc. Note that these measurements are correlated with a
correlation coefficient of 0.58. This represents a factor of 1.4 improvement in
the error on D_A relative to the pre-reconstruction case; a factor of 1.2
improvement is seen for H.Comment: 30 pages, 21 figures, accepted by MNRAS, updated to version accepted
by journa
The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: Analysis of potential systematics
We analyze the density field of galaxies observed by the Sloan Digital Sky
Survey (SDSS)-III Baryon Oscillation Spectroscopic Survey (BOSS) included in
the SDSS Data Release Nine (DR9). DR9 includes spectroscopic redshifts for over
400,000 galaxies spread over a footprint of 3,275 deg^2. We identify,
characterize, and mitigate the impact of sources of systematic uncertainty on
large-scale clustering measurements, both for angular moments of the
redshift-space correlation function and the spherically averaged power
spectrum, P(k), in order to ensure that robust cosmological constraints will be
obtained from these data. A correlation between the projected density of stars
and the higher redshift (0.43 < z < 0.7) galaxy sample (the `CMASS' sample) due
to imaging systematics imparts a systematic error that is larger than the
statistical error of the clustering measurements at scales s > 120h^-1Mpc or k
< 0.01hMpc^-1. We find that these errors can be ameliorated by weighting
galaxies based on their surface brightness and the local stellar density. We
use mock galaxy catalogs that simulate the CMASS selection function to
determine that randomly selecting galaxy redshifts in order to simulate the
radial selection function of a random sample imparts the least systematic error
on correlation function measurements and that this systematic error is
negligible for the spherically averaged correlation function. The methods we
recommend for the calculation of clustering measurements using the CMASS sample
are adopted in companion papers that locate the position of the baryon acoustic
oscillation feature (Anderson et al. 2012), constrain cosmological models using
the full shape of the correlation function (Sanchez et al. 2012), and measure
the rate of structure growth (Reid et al. 2012). (abridged)Comment: Matches version accepted by MNRAS. Clarifications and references have
been added. See companion papers that share the "The clustering of galaxies
in the SDSS-III Baryon Oscillation Spectroscopic Survey:" titl
The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: measurements of the growth of structure and expansion rate at z=0.57 from anisotropic clustering
We analyze the anisotropic clustering of massive galaxies from the Sloan
Digital Sky Survey III Baryon Oscillation Spectroscopic Survey (BOSS) Data
Release 9 (DR9) sample, which consists of 264,283 galaxies in the redshift
range 0.43 < z < 0.7 spanning 3,275 square degrees. Both peculiar velocities
and errors in the assumed redshift-distance relation ("Alcock-Paczynski
effect") generate correlations between clustering amplitude and orientation
with respect to the line-of-sight. Together with the sharp baryon acoustic
oscillation (BAO) standard ruler, our measurements of the broadband shape of
the monopole and quadrupole correlation functions simultaneously constrain the
comoving angular diameter distance (2190 +/- 61 Mpc) to z=0.57, the Hubble
expansion rate at z=0.57 (92.4 +/- 4.5 km/s/Mpc), and the growth rate of
structure at that same redshift (d sigma8/d ln a = 0.43 +/- 0.069). Our
analysis provides the best current direct determination of both DA and H in
galaxy clustering data using this technique. If we further assume a LCDM
expansion history, our growth constraint tightens to d sigma8/d ln a = 0.415
+/- 0.034. In combination with the cosmic microwave background, our
measurements of DA, H, and growth all separately require dark energy at z >
0.57, and when combined imply \Omega_{\Lambda} = 0.74 +/- 0.016, independent of
the Universe's evolution at z<0.57. In our companion paper (Samushia et al.
prep), we explore further cosmological implications of these observations.Comment: 19 pages, 11 figures, submitted to MNRAS, comments welcom
The 6dF Galaxy Survey: Baryon Acoustic Oscillations and the Local Hubble Constant
We analyse the large-scale correlation function of the 6dF Galaxy Survey
(6dFGS) and detect a Baryon Acoustic Oscillation (BAO) signal. The 6dFGS BAO
detection allows us to constrain the distance-redshift relation at z_{\rm eff}
= 0.106. We achieve a distance measure of D_V(z_{\rm eff}) = 456\pm27 Mpc and a
measurement of the distance ratio, r_s(z_d)/D_V(z_{\rm eff}) = 0.336\pm0.015
(4.5% precision), where r_s(z_d) is the sound horizon at the drag epoch z_d.
The low effective redshift of 6dFGS makes it a competitive and independent
alternative to Cepheids and low-z supernovae in constraining the Hubble
constant. We find a Hubble constant of H_0 = 67\pm3.2 km s^{-1} Mpc^{-1} (4.8%
precision) that depends only on the WMAP-7 calibration of the sound horizon and
on the galaxy clustering in 6dFGS. Compared to earlier BAO studies at higher
redshift, our analysis is less dependent on other cosmological parameters. The
sensitivity to H_0 can be used to break the degeneracy between the dark energy
equation of state parameter w and H_0 in the CMB data. We determine that w =
-0.97\pm0.13, using only WMAP-7 and BAO data from both 6dFGS and
\citet{Percival:2009xn}. We also discuss predictions for the large scale
correlation function of two future wide-angle surveys: the WALLABY blind H{\sc
I} survey (with the Australian SKA Pathfinder, ASKAP), and the proposed TAIPAN
all-southern-sky optical galaxy survey with the UK Schmidt Telescope (UKST). We
find that both surveys are very likely to yield detections of the BAO peak,
making WALLABY the first radio galaxy survey to do so. We also predict that
TAIPAN has the potential to constrain the Hubble constant with 3% precision.Comment: 18 pages, 17 figures, 3 table
Trabajo global y desigualdades en el mercado laboral
La globalización neoliberal fomentó una paradójica tensión entre las supuestas tendencias hacia la homogeneización y uniformización social, y la aparición de nuevas desigualdades sociales. La sociedad actual, lejos de experimentar las consecuencias del llamado "fin del trabajo", expresa sus efectos en cuanto a las formas d gestión laboral promovidas, la flexibilización, la desregularización de las relaciones laborales y la pérdida de calidad de las ocupaciones
Clinical and imaging correlates of amyloid deposition in dementia with Lewy bodies.
BACKGROUND: Amyloid deposition is common in dementia with Lewy bodies, but its pathophysiological significance is unclear. OBJECTIVE: The objective of this study was to investigate the relationship between amyloid deposition and clinical profile, gray matter volume, and brain perfusion in dementia with Lewy bodies. METHODS: Dementia with Lewy bodies (n = 37), Alzheimer's disease (n = 20), and controls (n = 20) underwent a thorough clinical assessment, 3T MRI, and early- and late-phase 18 F-Florbetapir PET-CT to assess cortical perfusion and amyloid deposition, respectively. Amyloid scans were visually categorized as positive or negative. Image analysis was carried out using statistical parametric mapping (SPM) 8. RESULTS: There were no significant differences between amyloid-positive and amyloid-negative dementia with Lewy bodies cases in age (P = .78), overall cognitive impairment (P = .83), level of functional impairment (P = .80), or any other clinical or cognitive scale. There were also no significant differences in hippocampal or gray matter volumes. However, amyloid-positive dementia with Lewy bodies cases had lower medial temporal lobe perfusion (P = .03) than amyloid-negative cases, although a combination of medial temporal lobe perfusion, hippocampal volume, and cognitive measures was unable to accurately predict amyloid status in dementia with Lewy bodies. CONCLUSIONS: Amyloid deposition was not associated with differences in clinical or neuropsychological profiles in dementia with Lewy bodies, but was associated with imaging evidence of medial temporal lobe dysfunction. The presence of amyloid in dementia with Lewy bodies cannot be identified on the basis of clinical and other imaging features and will require direct assessment via PET imaging or CSF. © 2018 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.Avid, Eli Lilly, NIHR Cambridge and Newcastle Biomedical Research Centr
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