Elisabeth Krause

First measurement of gravitational lensing by cosmic voids in SDSS

We report the first measurement of the diminutive lensing signal arising from matter underdensities associated with cosmic voids. While undetectable individually, by stacking the weak gravitational shear estimates around 901 voids detected in SDSS DR7 by Sutter et al. (2012a), we find substantial evidence for a depression of the lensing signal compared to the cosmic mean. This depression is most pronounced at the void radius, in agreement with analytical models of void matter profiles. Even with the largest void sample and imaging survey available today, we cannot put useful constraints on the radial dark-matter void profile. We invite independent investigations of our findings by releasing data and analysis code to the public at https://github.com/pmelchior/void-lensing.

The Weight of Emptiness: The Gravitational Lensing Signal of Stacked Voids

The upcoming new generation of spectroscopic galaxy redshift surveys will provide large samples of cosmic voids, large distinct, underdense structures in the universe. Combining these with future galaxy imaging surveys, we study the prospects of probing the underlying matter distribution in and around cosmic voids via the weak gravitational lensing effects of stacked voids, utilizing both shear and magnification information. The statistical precision is greatly improved by stacking a large number of voids along different lines of sight, even when taking into account the impact of inherent miscentering and projection effects. We show that Dark Energy Task Force Stage IV surveys, such as the Euclid satellite and the Large Synoptic Survey Telescope, should be able to detect the void lensing signal with sufficient precision from stacking abundant medium-sized voids, thus providing direct constraints on the matter density profile of voids independent of assumptions on galaxy bias.

Weak lensing power spectra for precision cosmology Multiple-deflection, reduced shear, and lensing bias corrections

It is usually assumed that the ellipticity power spectrum measured in weak lensing observations can be expressed as an integral over nthe underlying matter power spectrum. This is true at order O(Φ^2) in the gravitational potential. We extend the standard calculation, nconstructing all corrections to order O(Φ^4). There are four types of corrections: corrections to the lensing shear due to multiple-deflections; ncorrections due to the fact that shape distortions probe the reduced shear γ/(1 − κ) rather than the shear itself; corrections nassociated with the non-linear conversion of reduced shear to mean ellipticity; and corrections due to the fact that observational galaxy nselection and shear measurement is based on galaxy brightnesses and sizes which have been (de)magnified by lensing. We show how nthe previously considered corrections to the shear power spectrum correspond to terms in our analysis, and highlight new terms that nwere not previously identified. All correction terms are given explicitly as integrals over the matter power spectrum, bispectrum, and ntrispectrum, and are numerically evaluated for the case of sources at z = 1. We find agreement with previous works for the O(Φ^3) nterms. We find that for ambitious future surveys, the O(Φ^4) terms affect the power spectrum at the ~1−5σ level; they will thus need nto be accounted for, but are unlikely to represent a serious difficulty for weak lensing as a cosmological probe.

COSEBIs: Extracting the full E-/B-mode information from cosmic shear correlation functions

Context. Cosmic shear is considered one of the most powerful methods for studying the properties of dark energy in the Universe. As a standard method, the two-point correlation functions ξ_±(ϑ) of the cosmic shear field are used as statistical measures for the shear field. n nAims. In order to separate the observed shear into E- and B-modes, the latter being most likely produced by remaining systematics in the data set and/or intrinsic alignment effects, several statistics have been defined before. Here we aim at a complete E-/B-mode decomposition of the cosmic shear information contained in the ξ_± on a finite angular interval. n nMethods. We construct two sets of such E-/B-mode measures, namely Complete Orthogonal Sets of E-/B-mode Integrals (COSEBIs), characterized by weight functions between the ξ_± and the COSEBIs which are polynomials in ϑ or polynomials in ϑ, respectively. Considering the likelihood in cosmological parameter space, constructed from the COSEBIs, we study their information content. n nResults. We show that the information grows with the number of COSEBI modes taken into account, and that an asymptotic limit is reached which defines the maximum available information in the E-mode component of the ξ_±. We show that this limit is reached the earlier (i.e., for a smaller number of modes considered) the narrower the angular range is over which ξ_± are measured, and it is reached much earlier for logarithmic weight functions. For example, for on the interval 1 ≤ ϑ ≤ 400, the asymptotic limit for the parameter pair (Ω_m, σ_8) is reached for ~25 modes in the linear case, but already for 5 modes in the logarithmic case. The COSEBIs form a natural discrete set of quantities, which we suggest as method of choice in future cosmic shear likelihood analyses.

Testing Inflation with Large Scale Structure: Connecting Hopes with Reality

The statistics of primordial curvature fluctuations are our window into the period of inflation, where these fluctuations were generated. To date, the cosmic microwave background has been the dominant source of information about these perturbations. Large scale structure is however from where drastic improvements should originate. In this paper, we explain the theoretical motivations for pursuing such measurements and the challenges that lie ahead. In particular, we discuss and identify theoretical targets regarding the measurement of primordial non-Gaussianity. We argue that when quantified in terms of the local (equilateral) template amplitude

Accounting for Baryons in Cosmological Constraints from Cosmic Shear

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Mass and galaxy distributions of four massive galaxy clusters from Dark Energy Survey Science Verification data

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The Dark Energy Survey and operations: Year 1

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Merger-induced scatter and bias in the cluster mass–Sunyaev–Zel’dovich effect scaling relation

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Looking through the same lens: Shear calibration for LSST, Euclid, and WFIRST with stage 4 CMB lensing

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