Wide field weak lensing observations of A1835 and A2204

We present mass reconstructions from weak lensing for the galaxy clusters A1835 and A2204 over 34'x34' fields using data from the ESO/MPG Wide Field Imager. Using a background galaxy population of 22<R<25.5 we detect the gravitational shear of A1835 at 8.8 sigma significance, and obtain best-fit mass profiles of sigma_v=1233^{+66}_{-70} km/s for a singular isothermal sphere model and r_{200}=1550 h^{-1} kpc, c=2.96 for a `universal' CDM profile. Using a color-selected background galaxy population of 22<R<25.8 we detect the gravitational shear of A2204 at 7.2 sigma significance, and obtain best-fit mass profiles of sigma_v=1035^{+65}_{-71} km/s for a SIS model and r_{200}=1310 h^{-1} km/s, c=6.3 for a `universal' CDM profile. The gravitational shear at distances greater than 10' is significantly detected for both clusters. The best fit weak lensing cluster masses agree well with both X-ray and dynamical mass measurements, although the central concentration of A1835 is much lower in the weak lensing mass profile than that measured by recent Chandra results. We suggest that this lower concentration is most likely a combination of contamination of the 'background' galaxy population with cluster dwarf galaxies and the effect of a prolate or tri-axial cluster core with the major axis lying near the plane of the sky. We also detect a number of additional structures at moderate significance, some of which appear to be sub-haloes associated with the clusters.Comment: accepted to A&A, 14 pages, 13 figures, version with higher quality images can be found at http://www.uni-bonn.de/~clow

Weak lensing mass reconstructions of the ESO Distant Cluster Survey

We present weak lensing mass reconstructions for the 20 high-redshift clusters i n the ESO Distant Cluster Survey. The weak lensing analysis was performed on deep, 3-color optical images taken with VLT/FORS2, using a composite galaxy catalog with separate shape estimators measured in each passband. We find that the EDisCS sample is composed primarily of clusters that are less massive than t hose in current X-ray selected samples at similar redshifts, but that all of the fields are likely to contain massive clusters rather than superpositions of low mass groups. We find that 7 of the 20 fields have additional massive structures which are not associated with the clusters and which can affect the weak lensing mass determination. We compare the mass measurements of the remaining 13 clusters with luminosity measurements from cluster galaxies selected using photometric redshifts and find evidence of a dependence of the cluster mass-to-light ratio with redshift. Finally we determine the noise level in the shear measurements for the fields as a function of exposure time and seeing and demonstrate that future ground-based surveys which plan to perform deep optical imaging for use in weak lensing measurements must achieve point-spread functions smaller than a median of 0.6" FWHM.Comment: 35 pages, 24 figures, accepted to A&A, a version with better figure resolution can be found at http://www.mpa-garching.mpg.de/ediscs/papers.htm

Weak Lensing by High-Redshift Clusters of Galaxies II: Mean Redshift of the Faint Background Galaxy Population

We use weak lensing shear measurements of six z>0.5 clusters of galaxies to derive the mean lensing redshift of the background galaxies used to measure the shear. Five of these clusters are compared to X-ray mass models and verify a mean lensing redshift for a 23<R<26.3, R-I<0.9 background galaxy population in good agreement with photometric redshift surveys of the HDF-S. The lensing strength of the six clusters is also analyzed as a function of the magnitude of the background galaxies, and an increase in shear with increasing magnitude is detected at moderate significance. The change in the strength of the shear is presumed to be caused by an increase in the mean redshift of the background galaxies with increasing magnitude, and the degree of change detected is also in agreement with those in photometric redshift surveys of the HDF-S.Comment: 6 pages, 4 figures, accepted by A&

Wide field weak lensing observations of A1689

We present a mass profile for A1689 from 0.13 h^{-1} Mpc < r < 2 h^{-1} Mpc from a weak lensing analysis of a 34' x 34' R-band image from the ESO/MPG Wide Field Imager. We detect the gravitational shearing of a 23<R<25.5 background galaxy population even at the edge of the image with a 4 sigma significance, and find a two-dimensional mass reconstruction has a 13.4 sigma significance mass peak centered on the brightest cluster galaxy. This peak is well fit by both a 1028+-35 km/s singular isothermal sphere and a r200 = 1.28$ Mpc, c = 6 ``universal'' CDM profile. These mass measurements are lower than most of those derived by other means and we discuss possible reasons for weak lensing providing an underestimate of the true mass of the cluster. We find that the correction factors needed to reconcile the weak lensing mass models with the strong lensing Einstein radius would result is a much larger fraction of faint stars and foreground and cluster dwarf galaxies in the 23<R<25.5 object catalog then is seen in other fields

A mission to test the Pioneer anomaly: estimating the main systematic effects

We estimate the main systematic effects relevant in a mission to test and characterize the Pioneer anomaly through the flight formation concept, by launching probing spheres from a mother spacecraft and tracking their motion via laser ranging.Comment: 9 pages, 1 table, 2 figures; based on a talk presented by one of us (O.B.) at the 2nd. Pioneer Anomaly Group Meeting at the International Space Science Institute, 19-23 February 200

Weak lensing evidence for a filament between A222/A223

We present a weak lensing analysis and comparison to optical and X-ray maps of the close pair of massive clusters A222/223. Indications for a filamentary connection between the clusters are found and discussed.Comment: 6 pages, 1 figure. To appear in Proc. IAU Colloquium 195: Outskirts of Galaxy Clusters - Intense Life in the Suburbs. Version with higher resolution available at http://www.astro.uni-bonn.de/~dietrich/torino_proc.ps.g

Weak lensing observations of the "dark" cluster MG2016+112

We investigate the possible existence of a high-redshift (z=1) cluster of galaxies associated with the QSO lens system MG2016+112. From an ultra-deep R- and less deep V- and I-band Keck images and a K-band mosaic from UKIRT, we detect ten galaxies with colors consistent with the lensing galaxy within 225h^{-1} kpc of the z=1.01 lensing galaxy. This represents an overdensity of more than ten times the number density of galaxies with similar colors in the rest of the image. We also find a group of seven much fainter objects closely packed in a group only 27h^{-1} kpc north-west of the lensing galaxy. We perform a weak lensing analysis on faint galaxies in the R-band image and detect a mass peak of a size similar to the mass inferred from X-ray observations of the field, but located 64" northwest of the lensing galaxy. From the weak lensing data we rule out a similar sized mass peak centered on the lensing galaxy at the 2 sigma level.Comment: 9 pages, 10 figures, submitted to A&A version with figure 4 at higher resolution can be downloaded from http://www.mpa-garching.mpg.de/~clowe/mg2016aa.ps.g

Effects of asphericity and substructure on the determination of cluster mass with weak gravitational lensing

Weak gravitational lensing can be used to directly measure the mass along a line-of-sight without any dependence on the dynamical state of the mass, and thus can be used to measure the masses of clusters even if they are not relaxed. One common technique used to measure cluster masses is fitting azimuthally-averaged gravitational shear profiles with a spherical mass model. In this paper we quantify how asphericity and projected substructure in clusters can affect the virial mass and concentration measured with this technique by simulating weak lensing observations on 30 independent lines-of-sights through each of four high-resolution N-body cluster simulations. We find that the variations in the measured virial mass and concentration are of a size similar to the error expected in ideal weak lensing observations and are correlated, but that the virial mass and concentration of the mean shear profile agree well with that measured in three dimensional models of the clusters. The dominant effect causing the variations is the proximity of the line-of-sight to the major axis of the 3-D cluster mass distribution, with projected substructure only causing minor perturbations in the measured concentration. Finally we find that the best-fit "universal" CDM models used to fit the shear profiles over-predict the surface density of the clusters due to the cluster mass density falling off faster than the r^{-3} model assumption.Comment: 10 pages, 10 figures, accepted by MNRA

Beyond the pale?: the implications of the RSLG Report for non-CURL modern university libraries: Perspectives on the support libraries group: Final report

We have shown that the cluster-mass reconstruction method which combines strong and weak gravitational lensing data, developed in the first paper in the series, successfully reconstructs the mass distribution of a simulated cluster. In this paper we apply the method to the ground-based high-quality multi-colour data of RX J1347.5-114

Direct constraints on the dark matter self-interaction cross-section from the merging galaxy cluster 1E0657-56

We compare new maps of the hot gas, dark matter, and galaxies for 1E0657-56, a cluster with a rare, high-velocity merger occurring nearly in the plane of the sky. The X-ray observations reveal a bullet-like gas subcluster just exiting the collision site. A prominent bow shock gives an estimate of the subcluster velocity, 4500 km/s, which lies mostly in the plane of the sky. The optical image shows that the gas lags behind the subcluster galaxies. The weak-lensing mass map reveals a dark matter clump lying ahead of the collisional gas bullet, but coincident with the effectively collisionless galaxies. From these observations, one can directly estimate the cross-section of the dark matter self-interaction. That the dark matter is not fluid-like is seen directly in the X-ray -- lensing mass overlay; more quantitative limits can be derived from three simple independent arguments. The most sensitive constraint, sigma/m<1 cm^2/g, comes from the consistency of the subcluster mass-to-light ratio with the main cluster (and universal) value, which rules out a significant mass loss due to dark matter particle collisions. This limit excludes most of the 0.5-5 cm^2/g interval proposed to explain the flat mass profiles in galaxies. Our result is only an order-of-magnitude estimate which involves a number of simplifying, but always conservative, assumptions; stronger constraints may be derived using hydrodynamic simulations of this cluster.Comment: Text clarified; some numbers changed slightly for consistency with final version of the accompanying lensing paper. 6 pages, uses emulateapj. ApJ in pres