27 research outputs found

    Primordial non-Gaussianity with Angular correlation function: Integral constraint and validation for DES

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    Local primordial non-Gaussianity (PNG) is a promising observable of the underlying physics of inflation, characterised by fNLlocf_{\rm NL}^{\rm loc}. We present the methodology to measure fNLlocf_{\rm NL}^{\rm loc} from the Dark Energy Survey (DES) data using the 2-point angular correlation function (ACF) with scale-dependent bias. One of the focuses of the work is the integral constraint. This condition appears when estimating the mean number density of galaxies from the data and is key in obtaining unbiased fNLlocf_{\rm NL}^{\rm loc} constraints. The methods are analysed for two types of simulations: 246\sim 246 GOLIAT-PNG N-body small area simulations with fNLf_{\rm NL} equal to -100 and 100, and 1952 Gaussian ICE-COLA mocks with fNL=0f_{\rm NL}=0 that follow the DES angular and redshift distribution. We use the ensemble of GOLIAT-PNG mocks to show the importance of the integral constraint when measuring PNG, where we recover the fiducial values of fNLf_{\rm NL} within the 1σ1\sigma when including the integral constraint. In contrast, we found a bias of ΔfNL100\Delta f_{\rm NL}\sim 100 when not including it. For a DES-like scenario, we forecast a bias of ΔfNL23\Delta f_{\rm NL} \sim 23, equivalent to 1.8σ1.8\sigma, when not using the IC for a fiducial value of fNL=100f_{\rm NL}=100. We use the ICE-COLA mocks to validate our analysis in a realistic DES-like setup finding it robust to different analysis choices: best-fit estimator, the effect of IC, BAO damping, covariance, and scale choices. We forecast a measurement of fNLf_{\rm NL} within σ(fNL)=31\sigma(f_{\rm NL})=31 when using the DES-Y3 BAO sample, with the ACF in the 1 deg<θ<20 deg1\ {\rm deg}<\theta<20\ {\rm deg} range.Comment: Version after MNRAS reviewer comments. Improved discussion in Section 7. 16 pages, 11 figure

    LSST: from Science Drivers to Reference Design and Anticipated Data Products

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    (Abridged) We describe here the most ambitious survey currently planned in the optical, the Large Synoptic Survey Telescope (LSST). A vast array of science will be enabled by a single wide-deep-fast sky survey, and LSST will have unique survey capability in the faint time domain. The LSST design is driven by four main science themes: probing dark energy and dark matter, taking an inventory of the Solar System, exploring the transient optical sky, and mapping the Milky Way. LSST will be a wide-field ground-based system sited at Cerro Pach\'{o}n in northern Chile. The telescope will have an 8.4 m (6.5 m effective) primary mirror, a 9.6 deg2^2 field of view, and a 3.2 Gigapixel camera. The standard observing sequence will consist of pairs of 15-second exposures in a given field, with two such visits in each pointing in a given night. With these repeats, the LSST system is capable of imaging about 10,000 square degrees of sky in a single filter in three nights. The typical 5σ\sigma point-source depth in a single visit in rr will be 24.5\sim 24.5 (AB). The project is in the construction phase and will begin regular survey operations by 2022. The survey area will be contained within 30,000 deg2^2 with δ<+34.5\delta<+34.5^\circ, and will be imaged multiple times in six bands, ugrizyugrizy, covering the wavelength range 320--1050 nm. About 90\% of the observing time will be devoted to a deep-wide-fast survey mode which will uniformly observe a 18,000 deg2^2 region about 800 times (summed over all six bands) during the anticipated 10 years of operations, and yield a coadded map to r27.5r\sim27.5. The remaining 10\% of the observing time will be allocated to projects such as a Very Deep and Fast time domain survey. The goal is to make LSST data products, including a relational database of about 32 trillion observations of 40 billion objects, available to the public and scientists around the world.Comment: 57 pages, 32 color figures, version with high-resolution figures available from https://www.lsst.org/overvie

    The Vertical Structure of a Sediment-Stratified Turbolent Flow of Finite Depth

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    The vertical strucutre of a steady, horizontally uniform, sediment-stratified turbolent flow of finite depth is uniquely determined by four dimensionless parameters (the Rouse number, the relative friction velocity, the sediment Richardson number and the relative height), if the dependencies of the reference level and the reference suspended sediment concentration on the excess bottom shear stress are accounted for. The solution to the appropriate boundary-value problem is expected to show the property of complete similarity in the sediment Richardson number because the characteristic value of the sediment Richardson number is orders of magnitude greater than those of the other dimensionless parameters. This hypothesis is confirmed under conditions which are typical of estuaries and shallow waters by results of numerical experiments obtained using a b-L turbolence model. These results clearly demonstrate the dependence of the vertical mean velocity shear and suspended sediment concentration on the Rouse number and the relative friction velocity.JRC.(SAI)-Space Application Institut

    Universal Structure of the Sediment Bottom Logarithmic Layer

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    Abstract not availableJRC.(IRSA)-Institute For Remote Sensing Application

    A lagrangian Model of the Phytoplankton Dynamics in the Mauritanian Upwelling Zone

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    Abstract not availableJRC.(IRSA)-Institute For Remote Sensing Application

    Universal Structure of the Sediment-Stratified Bottom Logarithmic Layer

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    Abstract not availableJRC.(IRSA)-Institute For Remote Sensing Application

    Modelling the Thermal Surface Signature of Wave Breaking.

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    Abstract not availableJRC.(SAI)-Space Application Institut
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