The non-Gaussian matter power spectrum covariance in the halo model approach

Weak gravitational lensing is one of the most promising tools to analyze the nature of dark energy and dark matter. In order to constrain cosmological parameters with this method a good theoretical understanding of the underlying dark matter density field is necessary. This work provides an analytical treatment of higher-order correlation functions in the dark matter density field and compares the results obtained with numerical N-body simulations. The tool of choice is a semi-analytic halo model which combines results from perturbation theory and N-body simulations. The main emphasis of this work is on the fourth-order correlation function and its Fourier counterpart, the trispectrum, since it allows us to study the non-Gaussianities of the dark matter field and to calculate the full non-Gaussian covariance of the power spectrum. This provides a way to estimate the error and mode coupling in the dark matter power spectrum to higher accuracy than has been previously. After deriving an analytical expression for the expectation value of the three-dimensional and the convergence power spectrum covariance, we use the halo model to make explicit predictions for different cosmological models. Additionally, we analyze the impact of a stochastic concentration parameter on the non-Gaussian contribution to the power spectrum covariance. To minimize the computational effort to calculate the full non-Gaussian covariance, different approximations are studied within the halo model approach, and a fitting formula is derived that allows instant calculation of the convergence power spectrum covariance over a wide range of cosmological parameters.</p

Future internet enablers for VGI applications

This paper presents the authors experiences with the development of mobile Volunteered Geographic Information (VGI) applications in the context of the ENVIROFI project and Future Internet Public Private Partnership (FI-PPP) FP7 research programme.FI-PPP has an ambitious goal of developing a set of Generic FI Enablers (GEs) - software and hardware tools that will simplify development of thematic future internet applications. Our role in the programme was to provide requirements and assess the usability of the GEs from the point of view of the environmental usage area, In addition, we specified and developed three proof of concept implementations of environmental FI applications, and a set of specific environmental enablers (SEs) complementing the functionality offered by GEs. Rather than trying to rebuild the whole infrastructure of the Environmental Information Space (EIS), we concentrated on two aspects: (1) how to assure the existing and future EIS services and applications can be integrated and reused in FI context; and (2) how to profit from the GEs in future environmental applications.This paper concentrates on the GEs and SEs which were used in two of the ENVIROFI pilots which are representative for the emerging class of Volunteered Geographic Information (VGI) use-cases: one of them is pertinent to biodiversity and another to influence of weather and airborne pollution on users’ wellbeing. In VGI applications, the EIS and SensorWeb overlap with the Social web and potentially huge amounts of information from mobile citizens needs to be assessed and fused with the observations from official sources. On the whole, the authors are confident that the FI-PPP programme will greatly influence the EIS, but the paper also warns of the shortcomings in the current GE implementations and provides recommendations for further developments

Personalentwicklung und Mitarbeiterführung in Weiterbildungseinrichtungen

Der Studientext führt in die Grundlagen der Personalentwicklung und Mitarbeiterführung ein und überträgt diese auf die Arbeit in Weiterbildungseinrichtungen. Die Autorin beschreibt die Bedeutung und den Nutzen professioneller Personalarbeit und stellt die verschiedenen Führungsinstrumente und -techniken ausführlich vor. Auch Möglichkeiten der Erfolgskontrolle von Personalentwicklungsmaßnahmen werden aufgezeigt

Modeling of multimass systems torsionally deformed with variable inertia

Dynamic investigations of multimass discrete-continuous systems having variable moment of inertia are performed. The systems are torsionally deformed and consist of an arbitrary number of elastic elements connected by rigid bodies. The problem is nonlinear and it is linearized after appropriate transformations. It is shown that such problems can be investigated using the wave approach. Some analytical considerations and numerical calculations are done for a two-mass system with a special case of boundary conditions

Rezensionen

Rezension zu: 1) Dinkelaker, Jörg; Herrle, Matthias: Erziehungswissenschaftliche Videographie: eine Einführung. Wiesbaden: VS Verl. f. Sozialwissenschaften 2009. ISBN 978-3-531-16863-0. 2) Hugger, Kai-Uwe; Walber, Markus (Hg.): Digitale Lernwelten: Konzepte, Beispiele und Perspektiven. Wiesbaden: VS Verl. f. Sozialwissenschaften 2010. ISBN 978-3-531-16365-9. 3) Lenk, Christel: Freiberufler in der Weiterbildung: empirische Studie am Beispiel Hessen. Bielefeld: W. Bertelsmann Verl. 2010. ISBN 978-7639-3348-8 (Print), ISBN 978-7639-3348-5 (E-Book). 4) Merriam, Sharan B. u.a.: Non-Western Perspectives on Learning and Knowing. Malabar: Krieger Publ. Company 2007. ISBN 1-57524-280-X. 5) Meueler, Erhard: Die Türen des Käfigs: subjektorientierte Erwachsenenbildung. Baltmannsweiler: Schneider Verl. Hohengehren 2009. ISBN 978-3-8340-0527-4. 6) Neuber, Nils (Hg.): Informelles Lernen im Sport – Beiträge zur allgemeinen Bildungsdebatte. Wiesbaden: VS Verl. f. Sozialwissenschaften 2010. ISBN 978-3-531-17009-1. 7) Widany, Sarah: Lernen Erwachsener im Bildungsmonitoring: Operationalisierung der Weiterbildungsbeteiligung in empirischen Studien. Wiesbaden: VS Verl. f. Sozialwissenschaften 2009. ISBN 978-3-531-16896-8. 8) Zimmermann, Hildegard: Weiterbildung im späteren Erwerbsleben: empirische Befunde und Gestaltungsvorschläge. Bielefeld: W. Bertelsmann Verl. 2009. ISBN 978-3-7639-1132-4

A fitting formula for the non-Gaussian contribution to the lensing power spectrum covariance

Weak gravitational lensing is one of the most promising tools to investigate the equation-of-state of dark energy. In order to obtain reliable parameter estimations for current and future experiments, a good theoretical understanding of dark matter clustering is essential. Of particular interest is the statistical precision to which weak lensing observables, such as cosmic shear correlation functions, can be determined. We construct a fitting formula for the non-Gaussian part of the covariance of the lensing power spectrum. The Gaussian contribution to the covariance, which is proportional to the lensing power spectrum squared, and optionally shape noise can be included easily by adding their contributions. Starting from a canonical estimator for the dimensionless lensing power spectrum, we model first the covariance in the halo model approach including all four halo terms for one fiducial cosmology and then fit two polynomials to the expression found. On large scales, we use a first-order polynomial in the wave-numbers and dimensionless power spectra that goes asymptotically towards $1.1 C_{pt}$ for $\ell \to 0$, i.e., the result for the non-Gaussian part of the covariance using tree-level perturbation theory. On the other hand, for small scales we employ a second-order polynomial in the dimensionless power spectra for the fit. We obtain a fitting formula for the non-Gaussian contribution of the convergence power spectrum covariance that is accurate to 10% for the off-diagonal elements, and to 5% for the diagonal elements, in the range $50 \lesssim \ell \lesssim 5000$ and can be used for single source redshifts $z_{s} \in [0.5,2.0]$ in WMAP5-like cosmologies.Comment: 23 pages, 15 figures, submitted to A&

Weak lensing from space: first cosmological constraints from three-point shear statistics

We use weak lensing data from the Hubble Space Telescope COSMOS survey to measure the second- and third-moments of the cosmic shear field, estimated from about 450,000 galaxies with average redshift ~ 1.3. We measure two- and three-point shear statistics using a tree-code, dividing the signal in E, B and mixed components. We present a detection of the third-order moment of the aperture mass statistic and verify that the measurement is robust against systematic errors caused by point spread function (PSF) residuals and by the intrinsic alignments between galaxies. The amplitude of the measured three-point cosmic shear signal is in very good agreement with the predictions for a WMAP7 best-fit model, whereas the amplitudes of potential systematics are consistent with zero. We make use of three sets of large Lambda CDM simulations to test the accuracy of the cosmological predictions and to estimate the influence of the cosmology-dependent covariance. We perform a likelihood analysis using the measurement and find that the Omega_m-sigma_8 degeneracy direction is well fitted by the relation: sigma_8 (Omega_m/0.30)^(0.49)=0.78+0.11/-0.26. We present the first measurement of a more generalised three-point shear statistic and find a very good agreement with the WMAP7 best-fit cosmology. The cosmological interpretation of this measurement gives sigma_8 (Omega_m/0.30)^(0.46)=0.69 +0.08/-0.14. Furthermore, the combined likelihood analysis of this measurement with the measurement of the second order moment of the aperture mass improves the accuracy of the cosmological constraints, showing the high potential of this combination of measurements to infer cosmological constraints.Comment: 17 pages, 11 figures. MNRAS submitte

A New Data Compression Method and its Application to Cosmic Shear Analysis

Future large scale cosmological surveys will provide huge data sets whose analysis requires efficient data compression. Calculating accurate covariances is extremely challenging with increasing number of statistics used. Here we introduce a formalism for achieving efficient data compression, based on a local expansion of statistical measures around a fiducial cosmological model. We specifically apply and test this approach for the case of cosmic shear statistics. We demonstrate the performance of our approach, using a Fisher analysis on cosmic shear tomography described in terms of E-/B-mode separating statistics (COSEBIs). We show that our data compression is highly effective in extracting essentially the full cosmological information from a strongly reduced number of observables. Specifically, the number of statistics needed decreases by at least one order of magnitude relative to the COSEBIs, which already compress the data substantially compared to the shear two-point correlation functions. The efficiency appears to be affected only slightly if a highly inaccurate covariance is used for defining the compressed statistics, showing the robustness of the method. We conclude that an efficient data compression is achievable and that the number of compressed statistics depends on the number of model parameters. In addition, we study how well band powers can be obtained from measuring shear correlation functions over a finite interval of separations. We show the strong limitations on the possibility to construct top-hat filters in Fourier space, for which the real-space analog has a finite support, yielding strong bounds on the accuracy of band power estimates. The error on an estimated band-power is larger for a narrower filter and a smaller angular range which for relevant cases can be as large as 10%.Comment: 10 pages, 6 figure

The mass-concentration relationship of virialized halos and its impact on cosmological observables

A generic property of the cuspy simulated virialized halos in cold dark matter cosmogenies is that their concentration is inversely correlated with their mass. This behavior has also been confirmed in observations, although differences in the exact form and dispersion of this so-called mass-concentration relationship have been reported. Some observational studies of massive halos suggest that they are statistically over-concentrated with respect to the expectations of Lambda-CDM. Here we investigate the impact that various published mass-concentration relationships, both from simulations and derived from observations, would have on other cosmological observables, in particular considering upcoming surveys. We find that an integral measure of lensing shear, such as counts of peaks from halos, is very sensitive to the relationship between mass and concentration at fixed sigma-8, and the disparity between some reported fits is much larger than the impact of uncertainty in sigma-8 itself. We also briefly assess the impact of baryonic physics on cluster scale observables, using state-of-the-art simulations, concluding that it is unlikely to give rise to the high concentrations reported for some clusters.Comment: 12 pages, 9 figures, MNRAS accepte

Galaxy-galaxy lensing constraints on the relation between baryons and dark matter in galaxies in the Red Sequence Cluster Survey 2

We present the results of a study of weak gravitational lensing by galaxies using imaging data that were obtained as part of the second Red Sequence Cluster Survey (RCS2). In order to compare to the baryonic properties of the lenses we focus here on the ~300 square degrees that overlap with the DR7 of the SDSS. The depth and image quality of the RCS2 enables us to significantly improve upon earlier work for luminous galaxies at z>=0.3. Comparison with dynamical masses from the SDSS shows a good correlation with the lensing mass for early-type galaxies. For low luminosity (stellar mass) early-type galaxies we find a satellite fraction of ~40% which rapidly decreases to <10% with increasing luminosity (stellar mass). The satellite fraction of the late-types has a value in the range 0-15%. We find that early-types in the range 10^10<L_r<10^11.5 Lsun have virial masses that are about five times higher than those of late-type galaxies and that the mass scales as M_200 \propto L^2.34 +0.09 \ -0.16. We also measure the virial mass-to-light ratio, and find for L_200<10^11 Lsun a value of M_200/L_200=42+-10 for early-types, which increases for higher luminosities to values that are consistent with those observed for groups and clusters of galaxies. For late-type galaxies we find a lower value of M_200/L_200=17+-9. Our measurements also show that early- and late-type galaxies have comparable halo masses for stellar masses M_*<10^11 Msun, whereas the virial masses of early-type galaxies are higher for higher stellar masses. Finally, we determine the efficiency with which baryons have been converted into stars. Our results for early-type galaxies suggest a variation in efficiency with a minimum of ~10% for a stellar mass M_*,200=10^12 Msun. The results for the late-type galaxies are not well constrained, but do suggest a larger value. (abridged)Comment: 25 pages, 24 figures. Resubmitted to A&