92 research outputs found
Spatial matter density mapping of the STAGES Abell A901/2 supercluster field with 3D lensing
No full textWe present weak lensing data from the Hubble Space Telescope(HST)/Space Telescope A901/902 Galaxy Evolution Survey (STAGES) survey to study the three-dimensional spatial distribution of matter and galaxies in the Abell 901/902 supercluster complex. Our method improves over the existing 3D lensing mapping techniques by calibrating and removing redshift bias and accounting for the effects of the radial elongation of 3D structures. We also include the first detailed noise analysis of a 3D lensing map, showing that even with deep HST-quality data, only the most massive structures, for example M200≳ 1015M⊙h-1 at z∼ 0.8, can be resolved in 3D with any reasonable redshift accuracy (Δz≈ 0.15). We compare the lensing map to the stellar mass distribution and find luminous counterparts for all mass peaks detected with a peak significance >3σ. We see structures in and behind the z= 0.165 foreground supercluster, finding structure directly behind the A901b cluster at z∼ 0.6 and also behind the south-west (SW) group at z∼ 0.7. This 3D structure viewed in projection has no significant impact on recent mass estimates of A901b or the SW group components SWa and SWb. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS
Schlussbericht des Vorhaben
No full textIm Projekt "Tiefe HST Gravitationslinsenanalyse des massereichsten bekannten Galaxienhaufens bei Rotverschiebungen z>1: SPT-CLJ2106-5844“ wurden Hubble Space Telescope Daten des massiven Galaxienhaufens SPT-CLJ2106-5844 reduziert und wissenschaftlich ausgewertet. Hierzu wurden Datenreduktionsanpassungen bezüglich der Hintergrundmodellierung und astrometrischen Registrierung entwickelt. Farbmessungen basierend auf neuen WFC3/IR Mosaikdaten ermöglichten die Anwendungen eines alternativen Quellenselektionsschemas für die Analyse des schwachen Gravitationslinsensignals des Haufens. Aufgrund der begrenzten Tiefe der Farbdaten führte die Einbindung des alternativen Selektionsschemas nur zu einer moderaten Verkleinerung statistischer Unsicherheiten. Ein Fokus der weiteren Projektarbeiten lag auf der Reduktion systematischer Unsicherheiten und der Einschränkung kosmologischer Parameter und Skalierungsrelationsparameter unter Einbindung erweiterter Haufenstichproben und Gravitationslinsendatensätze. In Synergie mit weiteren in der Arbeitsgruppe durchgeführten Projekten publizierten wir Arbeiten zur verbesserten Korrektur von Massenmodellierungsfehlern und Analysen größerer Haufenstichproben. Zusätzlich entwickelten wir ein verbessertes Verfahren zur Abschätzung der Kontamination von Quellenstichproben durch Haufengalaxien im Falle nicht perfekter photometrischer Hintergrundselektionen und lieferten Beiträge zu aufbauenden und weiterführenden Studien.
Datei-Upload durch TIBIn the project "Tiefe HST Gravitationslinsenanalyse des massereichsten bekannten Galaxienhaufens bei Rotverschiebungen z>1: SPT-CLJ2106-5844“ Hubble Space Telescope (HST) observations of the massive galaxy cluster SPT-CLJ2106-5844 were reduced and scientifically analyzed. For this we developed advancements of the employed data reduction pipeline regarding the background modeling and astrometric alignment. Color measurements based on new WFC3/IR mosaic observations enabled the application of an alternative source selection scheme for the analysis of the weak gravitational lensing signal of the cluster. Given the limited depth of the color data, their inclusion led to only a moderate reduction of statistical uncertainties. Further project work focussed on the reduction of systematic uncertainties and the estimation of cosmological and scaling relation parameters when incorporating measurements from larger cluster and weak lensing samples. In synergy with further projects conducted in the research group, we published works regarding improved corrections for mass
modeling biases and analyses of larger cluster samples. Furthermore, we developed an improved method for the estimation of cluster member contamination in weak lensing source samples and contributed to further studies conducted within our collaboration
Editorial
No full textThis Special Letters Issue features the INTEGRAL observatory. About
one year after its successful launch, this series of 75 publications
describe the mission, the various instruments and their performance,
as well as first scientific results from the spacecraft, ranging from
gamma-ray bursts to Galactic sources. In order to produce this issue
in time, all parties involved have worked under great time
pressure. I would like to thank the authors and referees of these
articles for meeting such stringent deadlines and for their
cooperative attitude, and our publisher, EDP Sciences, for their
support and flexibility. A special thanks goes to Hendrik Hildebrandt,
Michael Mertens, and Tim Schrabback for their particular dedication
during the preparation of this Issue, working many hours overtime to
get that many Letters processed within two months (and in many cases,
on even much shorter time-scale). Furthermore, I thank Dr. Thierry
Courvoisier for his help during the preparation of this Issue.
Bonn, Sept. 24, 2003
Peter Schneider.
Measuring cosmological weak lensing using the Advanced Camera for Surveys on board the Hubble Space Telescope
No full textFollowing from the theory of General Relativity, light-bundles are deflected and differentially distorted while passing through the gravitational potential of matter inhomogeneities. The gravitational lensing effect caused by the large-scale matter distribution in the Universe is termed cosmological weak lensing, and provides a powerful probe of cosmology. By studying the distortions which are imprinted onto the observed shapes of distant galaxies, the statistical properties of the foreground density field can be constrained free of assumptions on the relation between luminous and dark matter. Due to the weakness of the effect, it is challenging to measure and can only be detected statistically from large ensembles of coherently lensed galaxies. In addition, careful correction for systematic effects is required, first of all for the image point-spread-function (PSF). In this PhD thesis we present a detailed cosmological weak lensing analysis using deep high-resolution images from the Advanced Camera for Surveys (ACS) on board the Hubble Space Telescope (HST). Including data from the ACS Parallel Cosmic Shear Survey, the HST/GEMS Survey, and the HST/COSMOS Survey, this data set constitutes the largest survey used to measure cosmological weak lensing from space today. In order to achieve the high accuracy required for weak lensing studies, we developed several upgrades for the data reduction pipeline including careful image registration, improved bad pixel masks, and an optimised weighting scheme. We also perform a thorough investigation of the ACS PSF and develop a new correction scheme for its spatial and temporal variations, which are caused by thermal breathing of the telescope. We present numerous tests of our shear measurement pipeline using simulated images from the STEP Programme, and demonstrate that it achieves a relative shear-measurement accuracy better than 2% for ACS-like images. We perform the analysis of the ACS data in two steps, starting with a pilot study, in which we test the capabilities of ACS for cosmological weak lensing measurements with early parallel observations and the combined GEMS and GOODS ACS mosaic of the Chandra Deep Field South (CDFS, 0.22 deg2). We perform a number of diagnostic tests indicating that the remaining level of systematics is consistent with zero for the GEMS and GOODS data confirming the success of our PSF correction scheme. For the parallel data we detect a low level of remaining systematics which we interpret to be caused by a lack of sufficient dithering of the data. Combining our shear estimate of the GEMS and GOODS observations using 96 galaxies arcmin-2 with the photometric redshift catalogue of the GOODS-MUSIC sample, we determine a local single field estimate for the mass power spectrum normalisation σ8=0.59+0.13-0.17(stat)±0.07(sys) (68% confidence assuming Gaussian sampling variance) at a fixed matter density Ωm=0.24 for a ΛCDM cosmology, where we marginalise over the uncertainty of the Hubble constant and the redshift distribution. This estimate agrees only marginally with the WMAP-3 result of σ8=0.761+0.049-0.048 (Spergel et al. 2007) and is significantly below values found by recent ground-based surveys. From this discrepancy we conclude that the CDFS is subject to strong sampling variance with a significant under-density of compact foreground structures. This is consistent with a recent study by Phleps et al. (2007), who find a strong deficiency of red galaxies in this field. In a second step we perform a preliminary cosmological weak lensing analysis of the HST/COSMOS Survey (1.64 deg2). The significantly increased statistical accuracy reveals previously undetectable residual systematic errors indicated by a significant B-mode signal. So far we have not been able to unambiguously identify their origin, but note that similar indications for remaining systematics have been found in an independent analysis of the same data by Massey et al. (2007). Using only B-mode-free scales (>1' in the shear two-point correlation function), we find σ8 = 0.71±0.09 (68% confidence) from COSMOS for a flat ΛCDM cosmology and fixed Ωm=0.24, where the error includes the uncertainties in the redshift distribution, the Hubble constant, and the shear calibration, as well as a Gaussian estimate for sampling variance. This result is in excellent agreement with the WMAP-3 constraints, but is significantly below the estimates found by Massey et al. (2007). In addition to the cosmological weak lensing analysis we present a reconstruction of the projected mass in the COSMOS field, as well as first results from a weak lensing analysis of the HST/STAGES Survey targeting the galaxy super-cluster Abell 901/902. Furthermore, we briefly summarise ACS studies of galaxy clusters, which make use of the developed data reduction and weak lensing pipeline
Validation of PSF Models for HST and Other Space-Based Observations
No full textForthcoming space-based observations will require high-quality point-spread function (PSF) models for weak gravitational lensing measurements. One approach to generating these models is using a wavefront model based on the known telescope optics. We present an empirical framework for validating such models to confirm that they match the actual PSF to within requirements by comparing the models to the observed light distributions of isolated stars. We apply this framework to Tiny Tim, the standard tool for generating model PSFs for the Hubble Space Telescope (HST), testing its models against images taken by HST's Advanced Camera for Surveys in the Wide Field Channel. We show that Tiny Tim's models, in the default configuration, differ significantly from the observed PSFs, most notably in their sizes. We find that the quality of Tiny Tim PSFs can be improved through fitting the full set of Zernike polynomial coefficients which characterise the optics, to the point where the practical significance of the difference between model and observed PSFs is negligible for most use cases, resulting in additive and multiplicative biases both of order approximately 4e-4. We also show that most of this improvement can be retained through using an updated set of Zernike coefficients, which we provide
Probing Galaxy Dark Matter Haloes in COSMOS with Weak Lensing Flexion
No full textCurrent theories of structure formation predict specific density profiles of galaxy dark matter haloes, and with weak gravitational lensing we can probe these profiles on several scales. On small scales, higher-order shape distortions known as flexion add significant detail to the weak lensing measurements. We present here the first detection of a galaxy-galaxy flexion signal in space-based data, obtained using a new Shapelets pipeline introduced here. We combine this higher-order lensing signal with shear to constrain the average density profile of the galaxy lenses in the Hubble Space Telescope COSMOS survey. We also show that light from nearby bright objects can significantly affect flexion measurements. After correcting for the influence of lens light, we show that the inclusion of flexion provides tighter constraints on density profiles than does shear alone. Finally we find an average density profile consistent with an isothermal sphere
Quantifying the impact of detection bias from blended galaxies on cosmic shear surveys
No full textIncreasingly large areas in cosmic shear surveys lead to a reduction in statistical errors, necessitating increasingly accurate control of systematic errors. Previous studies have investigated one of these systematic effects: image overlap with bright foreground galaxies may cause some distant source galaxies to remain undetected. Since this overlap is more likely to occur in regions of high foreground density – which tend to be the regions in which the shear is largest – this detection bias would cause an underestimation of the shear correlation function. This detection bias adds to the possible systematic of image blending, in which nearby pairs or multiplets of images render shear estimates more uncertain, and thus may cause a reduction in their statistical weight. Based on simulations with data from the Kilo-Degree Survey, we investigated the conditions under which images are not detected. We find an approximate analytic expression for the detection probability in terms of the separation and brightness ratio relative to the neighbouring galaxies. Applying this fitting formula to weak-lensing ray tracing through the galaxy distribution in the Millennium Simulation, we estimate that the detection bias alone causes an underestimation of by almost 2%, and therefore cannot be neglected in current and forthcoming cosmic shear surveys
Weak lensing mass bias and the alignment of center proxies
No full textGalaxy cluster masses derived from observations of weak lensing suffer from a
number of biases affecting the accuracy of mass-observable relations calibrated
from such observations. In particular, the choice of the cluster center plays a
prominent role in biasing inferred masses. In the past, empirical miscentring
distributions have been used to address this issue. Using hydro-dynamical
simulations, we aim to test the accuracy of weak lensing mass bias predictions
based on such miscentring distributions by comparing the results to mass biases
computed directly using intra-cluster medium (ICM)-based centers from the same
simulation. We construct models for fitting masses to both centered and
miscentered Navarro-Frenk-White profiles of reduced shear, and model the
resulting distributions of mass bias with normal and log-normal distributions.
We find that the standard approach of using miscentring distributions leads to
an over-estimation of cluster masses at levels of between 2\% and 6\% when
compared to the analysis in which actual simulated ICM centers are used, even
when the underlying miscentring distributions match in terms of the miscentring
amplitude. We find that neither log-normal nor normal distributions are
generally reliable for approximating the shapes of the mass bias distributions,
regardless of whether a centered or miscentered radial model is used.Comment: 15 pages, 9 figures, submitted to MNRA
Deep Lensing Posterior Samples
No full textThis archive contains the main results of Probabilistic Mass Mapping with Neural Score Estimation (Remy et al. 2022).
It consists of convergence posterior samples computed with our method from different fields (HSC/ACS COSMOS, mocked shear field computed from \kappaTNG map, mocked shear field with added NFW cluster).
It also contains the trained neural network weights we used.
The details of the creation of this dataset and how to use it to reproduce the plots of the paper can be found at https://github.com/cosmoStat/jax-lensing
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