33 research outputs found
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The LSST DESC data challenge 1: Generation and analysis of synthetic images for next-generation surveys
Data Challenge 1 (DC1) is the first synthetic data set produced by the Rubin Observatory Legacy Survey of Space and Time (LSST) Dark Energy Science Collaboration (DESC). DC1 is designed to develop and validate data reduction and analysis and to study the impact of systematic effects that will affect the LSST data set. DC1 is comprised of r-band observations of 40 deg2 to 10 yr LSST depth. We present each stage of the simulation and analysis process: (a) generation, by synthesizing sources from cosmological N-body simulations in individual sensor-visit images with different observing conditions; (b) reduction using a development version of the LSST Science Pipelines; and (c) matching to the input cosmological catalogue for validation and testing. We verify that testable LSST requirements pass within the fidelity of DC1. We establish a selection procedure that produces a sufficiently clean extragalactic sample for clustering analyses and we discuss residual sample contamination, including contributions from inefficiency in star-galaxy separation and imperfect deblending. We compute the galaxy power spectrum on the simulated field and conclude that: (i) survey properties have an impact of 50 per cent of the statistical uncertainty for the scales and models used in DC1; (ii) a selection to eliminate artefacts in the catalogues is necessary to avoid biases in the measured clustering; and (iii) the presence of bright objects has a significant impact (2-6) in the estimated power spectra at small scales (> 1200), highlighting the impact of blending in studies at small angular scales in LSST
Confirmation of general relativity on large scales from weak lensing and galaxy velocities
Although general relativity underlies modern cosmology, its applicability on
cosmological length scales has yet to be stringently tested. Such a test has
recently been proposed, using a quantity, EG, that combines measures of
large-scale gravitational lensing, galaxy clustering and structure growth rate.
The combination is insensitive to 'galaxy bias' (the difference between the
clustering of visible galaxies and invisible dark matter) and is thus robust to
the uncertainty in this parameter. Modified theories of gravity generally
predict values of EG different from the general relativistic prediction
because, in these theories, the 'gravitational slip' (the difference between
the two potentials that describe perturbations in the gravitational metric) is
non-zero, which leads to changes in the growth of structure and the strength of
the gravitational lensing effect3. Here we report that EG = 0.39 +/- 0.06 on
length scales of tens of megaparsecs, in agreement with the general
relativistic prediction of EG 0.4. The measured value excludes a
model within the tensor-vector-scalar gravity theory, which modifies both
Newtonian and Einstein gravity. However, the relatively large uncertainty still
permits models within f(R) theory, which is an extension of general relativity.
A fivefold decrease in uncertainty is needed to rule out these models.Comment: Submitted version; 13 pages, 2 figures. Accepted version and
supplementary material are available at:
http://www.nature.com/nature/journal/v464/n7286/full/nature08857.html
Microbial changes linked to the accelerated degradation of the herbicide atrazine in a range of temperate soils
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The LSST DESC data challenge 1: Generation and analysis of synthetic images for next-generation surveys
Data Challenge 1 (DC1) is the first synthetic data set produced by the Rubin Observatory Legacy Survey of Space and Time (LSST) Dark Energy Science Collaboration (DESC). DC1 is designed to develop and validate data reduction and analysis and to study the impact of systematic effects that will affect the LSST data set. DC1 is comprised of r-band observations of 40 deg2 to 10 yr LSST depth. We present each stage of the simulation and analysis process: (a) generation, by synthesizing sources from cosmological N-body simulations in individual sensor-visit images with different observing conditions; (b) reduction using a development version of the LSST Science Pipelines; and (c) matching to the input cosmological catalogue for validation and testing. We verify that testable LSST requirements pass within the fidelity of DC1. We establish a selection procedure that produces a sufficiently clean extragalactic sample for clustering analyses and we discuss residual sample contamination, including contributions from inefficiency in star-galaxy separation and imperfect deblending. We compute the galaxy power spectrum on the simulated field and conclude that: (i) survey properties have an impact of 50 per cent of the statistical uncertainty for the scales and models used in DC1; (ii) a selection to eliminate artefacts in the catalogues is necessary to avoid biases in the measured clustering; and (iii) the presence of bright objects has a significant impact (2-6) in the estimated power spectra at small scales (> 1200), highlighting the impact of blending in studies at small angular scales in LSST
Verificação da interferência das disfunções temporomandibulares na articulação da fala: queixas e caracterização dos movimentos mandibulares
The use of magnetic resonance imaging in acute knee injuries can be reduced by non-physician expert clinics
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The sdss-iii baryon oscillation spectroscopic survey: The quasar luminosity function from data release nine
We present a new measurement of the optical quasar luminosity function (QLF), using data from the Sloan Digital Sky Survey-III: Baryon Oscillation Spectroscopic Survey (SDSS-III: BOSS). From the SDSS-III Data Release Nine, a uniform sample of 22,301 i ≲ 21.8 quasars are selected over an area of 2236 deg2, with confirmed spectroscopic redshifts between 2.2 < z < 3.5, filling in a key part of the luminosity-redshift plane for optical quasar studies. The completeness of the survey is derived through simulated quasar photometry, and this completeness estimate is checked using a sample of quasars selected by their photometric variability within the BOSS footprint. We investigate the level of systematics associated with our quasar sample using the simulations, in the process generating color-redshift relations and a new quasar K-correction. We probe the faint end of the QLF to Mi (z = 2.2) ≈ -24.5 and see a clear break in the QLF at all redshifts up to z = 3.5. A log-linear relation (in log Φ*-M*) for a luminosity evolution and density evolution model is found to adequately describe our data within the range 2.2 < z < 3.5; across this interval the break luminosity increases by a factor of ∼2.6 while Φ* declines by a factor of ∼8. At z ≲ 2.2 our data are reasonably well fit by a pure luminosity evolution model, and only a weak signature of "AGN downsizing" is seen, in line with recent studies of the hard X-ray luminosity function. We compare our measured QLF to a number of theoretical models and find that models making a variety of assumptions about quasar triggering and halo occupation can fit our data over a wide range of redshifts and luminosities. © 2013. The American Astronomical Society. All rights reserved