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Featured researches published by E. Krause.


Physical Review D | 2016

Cosmic shear measurements with Dark Energy Survey science verification data

A. K. Romer; M. R. Becker; M. A. Troxel; N. MacCrann; E. Krause; T. F. Eifler; O. Friedrich; Andrina Nicola; Alexandre Refregier

We present measurements of weak gravitational lensing cosmic shear two-point statistics using Dark Energy Survey Science Verification data. We demonstrate that our results are robust to the choice of shear measurement pipeline, either ngmix or im3shape, and robust to the choice of two-point statistic, including both real and Fourier-space statistics. Our results pass a suite of null tests including tests for B-mode contamination and direct tests for any dependence of the two-point functions on a set of 16 observing conditions and galaxy properties, such as seeing, airmass, galaxy color, galaxy magnitude, etc. We furthermore use a large suite of simulations to compute the covariance matrix of the cosmic shear measurements and assign statistical significance to our null tests. We find that our covariance matrix is consistent with the halo model prediction, indicating that it has the appropriate level of halo sample variance. We compare the same jackknife procedure applied to the data and the simulations in order to search for additional sources of noise not captured by the simulations. We find no statistically significant extra sources of noise in the data. The overall detection significance with tomography for our highest source density catalog is 9.7 sigma . Cosmological constraints from the measurements in this work are presented in a companion paper [DES et al., Phys. Rev. D 94, 022001 (2016).].


Monthly Notices of the Royal Astronomical Society | 2016

Cosmology constraints from shear peak statistics in Dark Energy Survey Science Verification data

Tomasz Kacprzak; D. Kirk; O. Friedrich; Adam Amara; Alexandre Refregier; Laura Marian; J. P. Dietrich; E. Suchyta; J. Aleksić; David Bacon; M. R. Becker; C. Bonnett; Sarah Bridle; C. L. Chang; T. F. Eifler; W. G. Hartley; Eric Huff; E. Krause; N. MacCrann; P. Melchior; Andrina Nicola; S. Samuroff; E. Sheldon; M. A. Troxel; J. Weller; J. Zuntz; T. M. C. Abbott; F. B. Abdalla; Robert Armstrong; A. Benoit-Lévy

Shear peak statistics has gained a lot of attention recently as a practical alternative to the two-point statistics for constraining cosmological parameters. We perform a shear peak statistics analysis of the Dark Energy Survey (DES) Science Verification (SV) data, using weak gravitational lensing measurements from a 139 deg² field. We measure the abundance of peaks identified in aperture mass maps, as a function of their signal-to-noise ratio, in the signal-to-noise range 0 4 would require significant corrections, which is why we do not include them in our analysis. We compare our results to the cosmological constraints from the two-point analysis on the SV field and find them to be in good agreement in both the central value and its uncertainty. We discuss prospects for future peak statistics analysis with upcoming DES data.


Monthly Notices of the Royal Astronomical Society | 2017

CosmoLike - Cosmological Likelihood Analyses for Photometric Galaxy Surveys

E. Krause; T. F. Eifler

We explore strategies to extract cosmological constraints from a joint analysis of cosmic shear, galaxy–galaxy lensing, galaxy clustering, cluster number counts and cluster weak lensing. We utilize the COSMOLIKE software to simulate results from a Large Synoptic Survey Telescope (LSST) like data set, specifically, we (1) compare individual and joint analyses of the different probes, (2) vary the selection criteria for lens and source galaxies, (3) investigate the impact of blending, (4) investigate the impact of the assumed cosmological model in multiprobe covariances, (6) quantify information content as a function of scales and (7) explore the impact of intrinsic galaxy alignment in a multiprobe context. Our analyses account for all cross-correlations within and across probes and include the higher-order (non-Gaussian) terms in the multiprobe covariance matrix. We simultaneously model cosmological parameters and a variety of systematics, e.g. uncertainties arising from shear and photo-z calibration, cluster mass-observable relation, galaxy intrinsic alignment and galaxy bias (up to 54 parameters altogether). We highlight two results: first, increasing the number density of source galaxies by ∼30 per cent, which corresponds to solving blending for LSST, only gains little information. Secondly, including small scales in clustering and galaxy–galaxy lensing, by utilizing halo occupation distribution models, can substantially boost cosmological constraining power.


Monthly Notices of the Royal Astronomical Society | 2016

The impact of intrinsic alignment on current and future cosmic shear surveys

E. Krause; T. F. Eifler; J. Blazek

Intrinsic alignment (IA) of source galaxies is one of the major astrophysical systematics for ongoing and future weak lensing surveys. This paper presents the first forecasts of the impact of IA on cosmic shear measurements for current and future surveys (DES, Euclid, LSST, WFIRST) using simulated likelihood analyses and realistic covariances that include higher-order moments of the density field in the computation. We consider a range of possible IA scenarios and test mitigation schemes, which parameterize IA by the fraction of red galaxies, normalization, luminosity and redshift dependence of the IA signal (for a subset we consider joint IA and photo-z uncertainties). Compared to previous studies we find smaller biases in time-dependent dark energy models if IA is ignored in the analysis; the amplitude and significance of these biases vary as a function of survey properties (depth, statistical uncertainties), luminosity function, and IA scenario: Due to its small statistical errors and relatively shallow observing strategy Euclid is significantly impacted by IA. LSST and WFIRST benefit from their increased survey depth, while the larger statistical errors for DES decrease IAs relative impact on cosmological parameters. The proposed IA mitigation scheme removes parameter biases due to IA for DES, LSST, and WFIRST even if the shape of the IA power spectrum is only poorly known; successful IA mitigation for Euclid requires more prior information. We explore several alternative IA mitigation strategies for Euclid; in the absence of alignment of blue galaxies we recommend the exclusion of red (IA contaminated) galaxies in cosmic shear analyses. We find that even a reduction of 20% in the number density of galaxies only leads to a 4-10% loss in cosmological constraining power.


Monthly Notices of the Royal Astronomical Society | 2017

Cosmic voids and void lensing in the Dark Energy Survey Science Verification data

C. Sánchez; Joseph Clampitt; A. Kovács; Bhuvnesh Jain; J. García-Bellido; Seshadri Nadathur; D. Gruen; Nico Hamaus; Dragan Huterer; P. Vielzeuf; Adam Amara; C. Bonnett; J. DeRose; W. G. Hartley; M. Jarvis; Ofer Lahav; R. Miquel; Eduardo Rozo; E. S. Rykoff; E. Sheldon; Risa H. Wechsler; J. Zuntz; T. M. C. Abbott; F. B. Abdalla; J. Annis; A. Benoit-Lévy; G. M. Bernstein; Rebecca A. Bernstein; E. Bertin; David J. Brooks

Galaxies and their dark matter halos populate a complicated filamentary network around large, nearly empty regions known as cosmic voids. Cosmic voids are usually identified in spectroscopic galaxy surveys, where 3D information about the large-scale structure of the Universe is available. Although an increasing amount of photometric data is being produced, its potential for void studies is limited since photometric redshifts induce line-of-sight position errors of ∼50 Mpc/h or more that can render many voids undetectable. In this paper we present a new void finder designed for photometric surveys, validate it using simulations, and apply it to the high-quality photo-z redMaGiC galaxy sample of the Dark Energy Survey Science Verification (DES-SV) data. The algorithm works by projecting galaxies into 2D slices and finding voids in the smoothed 2D galaxy density field of the slice. Fixing the line-of-sight size of the slices to be at least twice the photo-z scatter, the number of voids found in these projected slices of simulated spectroscopic and photometric galaxy catalogs is within 20% for all transverse void sizes, and indistinguishable for the largest voids of radius ∼70 Mpc/h and larger. The positions, radii, and projected galaxy profiles of photometric voids also accurately match the spectroscopic void sample. Applying the algorithm to the DES-SV data in the redshift range 0.2<z<0.8 , we identify 87 voids with comoving radii spanning the range 18-120 Mpc/h , and carry out a stacked weak lensing measurement. With a significance of 4.4σ , the lensing measurement confirms the voids are truly underdense in the matter field and hence not a product of Poisson noise, tracer density effects or systematics in the data. It also demonstrates, for the first time in real data, the viability of void lensing studies in photometric surveys.


The Astrophysical Journal | 2017

Farthest neighbor: the distant Milky Way satellite Eridanus II*

T. S. Li; J. D. Simon; A. Drlica-Wagner; K. Bechtol; Mei-Yu Wang; J. García-Bellido; Joshua A. Frieman; J. L. Marshall; D. J. James; Louis E. Strigari; A. B. Pace; E. Balbinot; Y. Zhang; T. M. C. Abbott; S. Allam; A. Benoit-Lévy; G. M. Bernstein; E. Bertin; David J. Brooks; D. L. Burke; A. Carnero Rosell; M. Carrasco Kind; J. Carretero; C. E. Cunha; C. B. D’Andrea; L. N. da Costa; D. L. DePoy; S. Desai; H. T. Diehl; T. F. Eifler

We present Magellan/IMACS spectroscopy of the recently discovered Milky Way satellite Eridanus II (Eri II). We identify 28 member stars in Eri II, from which we measure a systemic radial velocity of nu(hel)= 75.6 +/- 1.3(stat.) +/- 2.0 (sys.) km s(-1) and a velocity dispersion of 6.9(-0.9)(+1.2) km s(-1). Assuming that Eri. II is a dispersion-supported system in dynamical equilibrium, we derive a mass within the half-light radius of 1.2(-0.3)(+0.4) x 10(7) M-circle dot, indicating a mass-tolight ratio of 420(-140)(+210) M-circle dot/L-circle dot and confirming that it is a dark matter-dominated dwarf galaxy. From the equivalent width measurements of the Ca triplet lines of 16 red giant member stars, we derive a mean metallicity of [ Fe/H] = -2.38 +/- 0.13 and a metallicity dispersion of sigma[Fe/H]= 0.47(-0.09)(+0.12). The velocity of Eri. II in the Galactic standard of rest frame is nu(GSR) = -66.6 km s(-1), indicating that either Eri. II is falling into the Milky Way potential for the first time or that it has passed the apocenter of its orbit on a subsequent passage. At a Galactocentric distance of similar to 370 kpc, Eri II is one of the Milky Ways most distant satellites known. Additionally, we show that the bright blue stars previously suggested to be a young stellar population are not associated with Eri. II. The lack of gas and recent star formation in Eri II is surprising given its mass and distance from the Milky Way, and may place constraints on models of quenching in dwarf galaxies and on the distribution of hot gas in the Milky Way halo. Furthermore, the large velocity dispersion of Eri II can be combined with the existence of a central star cluster to constrain massive compact halo object dark matter with mass greater than or similar to 10 M-circle dot.


Monthly Notices of the Royal Astronomical Society | 2017

Galaxy-galaxy lensing in the Dark Energy Survey Science Verification data

Joseph Clampitt; C. Sánchez; Juliana Kwan; E. Krause; N. MacCrann; Youngsoo Park; M. A. Troxel; Bhuvnesh Jain; Eduardo Rozo; E. S. Rykoff; Risa H. Wechsler; J. Blazek; C. Bonnett; M. Crocce; Y. Fang; E. Gaztanaga; D. Gruen; M. Jarvis; R. Miquel; J. Prat; A. Ross; E. Sheldon; J. Zuntz; T. M. C. Abbott; F. B. Abdalla; Robert Armstrong; M. R. Becker; A. Benoit-Lévy; G. M. Bernstein; E. Bertin

We present galaxy-galaxy lensing results from 139 deg(2) of Dark Energy Survey (DES) Science Verification (SV) data. Our lens sample consists of red galaxies, known as redMaGiC, which are specifically selected to have a low photometric redshift error and outlier rate. The lensing measurement has a total signal-to-noise ratio of 29 over scales 0.09 < R < 15 Mpc h(-1), including all lenses over a wide redshift range 0.2 < z < 0.8. Dividing the lenses into three redshift bins for this constant moving number density sample, we find no evidence for evolution in the halo mass with redshift. We obtain consistent results for the lensing measurement with two independent shear pipelines, NGMIX and IM3SHAPE. We perform a number of null tests on the shear and photometric redshift catalogues and quantify resulting systematic uncertainties. Covariances from jackknife subsamples of the data are validated with a suite of 50 mock surveys. The result and systematic checks in this work provide a critical input for future cosmological and galaxy evolution studies with the DES data and redMaGiC galaxy samples. We fit a halo occupation distribution (HOD) model, and demonstrate that our data constrain the mean halo mass of the lens galaxies, despite strong degeneracies between individual HOD parameters.


Monthly Notices of the Royal Astronomical Society | 2018

Dark Energy Survey Year 1 results: the impact of galaxy neighbours on weak lensing cosmology with IM3SHAPE

S. Samuroff; Sarah Bridle; J Zuntz; M. A. Troxel; D. Gruen; R. P. Rollins; G. M. Bernstein; T. F. Eifler; E M Huff; Tomasz Kacprzak; E. Krause; N MacCrann; F. B. Abdalla; S. Allam; J. Annis; K. Bechtol; A. Benoit-Lévy; E. Bertin; D. Brooks; E. Buckley-Geer; A. Carnero Rosell; M. Carrasco Kind; J. Carretero; M. Crocce; C. B. D'Andrea; L. N. da Costa; C. Davis; S. Desai; P. Doel; A. Fausti Neto

We use a suite of simulated images based on Year 1 of the Dark Energy Survey to explore the impact of galaxy neighbours on shape measurement and shear cosmology. The HOOPOE image simulations include realistic blending, galaxy positions, and spatial variations in depth and point spread function properties. Using the IM3SHAPE maximum-likelihood shape measurement code, we identify four mechanisms by which neighbours can have a non-negligible influence on shear estimation. These effects, if ignored, would contribute a net multiplicative bias of m ~ 0.03-0.09 in the Year One of the Dark Energy Survey (DES Y1) IM3SHAPE catalogue, though the precise impact will be dependent on both the measurement code and the selection cuts applied. This can be reduced to percentage level or less by removing objects with close neighbours, at a cost to the effective number density of galaxies neff of 30 per cent. We use the cosmological inference pipeline of DES Y1 to explore the cosmological implications of neighbour bias and show that omitting blending from the calibration simulation for DES Y1 would bias the inferred clustering amplitude S 8 ≡ σ 8 (Ω m /0.3) 0.5 by 2σ towards low values. Finally, we use the HOOPOE simulations to test the effect of neighbour-induced spatial correlations in the multiplicative bias.We find the impact on the recovered S 8 of ignoring such correlations to be subdominant to statistical error at the current level of precision.


The Astrophysical Journal | 2017

An r-process Enhanced Star in the Dwarf Galaxy Tucana III

Terese T. Hansen; J. D. Simon; J. L. Marshall; T. S. Li; Daniela Carollo; D. L. DePoy; D. Q. Nagasawa; R. A. Bernstein; A. Drlica-Wagner; F. B. Abdalla; S. Allam; J. Annis; K. Bechtol; A. Benoit-Lévy; David J. Brooks; E. Buckley-Geer; A. Carnero Rosell; M. Carrasco Kind; J. Carretero; C. E. Cunha; L. N. da Costa; S. Desai; T. F. Eifler; A. Fausti Neto; B. Flaugher; Joshua A. Frieman; J. García-Bellido; E. Gaztanaga; D. W. Gerdes; D. Gruen

Chemically peculiar stars in dwarf galaxies provide a window for exploring the birth environment of stars with varying chemical enrichment. We present a chemical abundance analysis of the brightest star in the newly discovered ultra-faint dwarf galaxy candidate Tucana III. Because it is particularly bright for a star in an ultra-faint Milky Way (MW) satellite, we are able to measure the abundance of 28 elements, including 13 neutron-capture species. This star, DES J235532.66−593114.9 (DES J235532), shows a mild enhancement in neutron-capture elements associated with the r-process and can be classified as an r-I star. DES J235532 is the first r-I star to be discovered in an ultra-faint satellite, and Tuc III is the second extremely low-luminosity system found to contain r-process enriched material, after Reticulum II. Comparison of the abundance pattern of DES J235532 with r-I and r-II stars found in other dwarf galaxies and in the MW halo suggests a common astrophysical origin for the neutron-capture elements seen in all r-process enhanced stars. We explore both internal and external scenarios for the r-process enrichment of Tuc III and show that with abundance patterns for additional stars, it should be possible to distinguish between them.


Physical Review D | 2016

Joint analysis of galaxy-galaxy lensing and galaxy clustering: Methodology and forecasts for Dark Energy Survey

Youngsoo Park; E. Krause; Scott Dodelson; Bhuvnesh Jain; Adam Amara; M. R. Becker; Sarah Bridle; Joseph Clampitt; M. Crocce; P. Fosalba; E. Gaztanaga; K. Honscheid; Eduardo Rozo; F. Sobreira; C. Sanchez; Risa H. Wechsler; T. D. Abbott; F.B. Abdalla; S. Allam; A. Benoit-Lévy; E. Bertin; David J. Brooks; E. Buckley-Geer; D. L. Burke; A. Carnero Rosell; M. Carrasco Kind; J. Carretero; Francisco J. Castander; L. N. da Costa; D. L. DePoy

The joint analysis of galaxy-galaxy lensing and galaxy clustering is a promising method for inferring the growth function of large-scale structure. Anticipating a near future application of this analysis to Dark Energy Survey (DES) measurements of galaxy positions and shapes, we develop a practical approach to modeling the assumptions and systematic effects affecting the joint analysis of small-scale galaxy-galaxy lensing and large-scale galaxy clustering. Introducing parameters that characterize the halo occupation distribution (HOD), photometric redshift uncertainties, and shear measurement errors, we study how external priors on different subsets of these parameters affect our growth constraints. Degeneracies within the HOD model, as well as between the HOD and the growth function, are identified as the dominant source of complication, with other systematic effects being subdominant. The impact of HOD parameters and their degeneracies necessitate the detailed joint modeling of the galaxy sample that we employ. We conclude that DES data will provide powerful constraints on the evolution of structure growth in the Universe, conservatively/optimistically constraining the growth function to 7.9%/4.8% with its first-year data that cover over 1000 square degrees, and to 3.9%/2.3% with its full five-year data that will survey 5000 square degrees, including both statistical and systematic uncertainties.

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David J. Brooks

University College London

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A. Benoit-Lévy

Institut d'Astrophysique de Paris

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E. Bertin

Institut d'Astrophysique de Paris

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L. N. da Costa

European Southern Observatory

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