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

Weak Lensing by High-Redshift Clusters of Galaxies - I: Cluster Mass Reconstruction

We present the results of a weak lensing survey of six high-redshift (z > 0.5), X-ray selected clusters of galaxies. We have obtained ultra-deep R-band images of each cluster with the Keck Telescope, and have measured a weak lensing signal from each cluster. From the background galaxy ellipticities we create two-dimensional maps of the surface mass density of each cluster. We find that the substructure seen in the mass reconstructions typically agree well with substructure in both the cluster galaxy distributions and X-ray images of the clusters. We also measure the one-dimensional radial profiles of the lensing signals and fit these with both isothermal spheres and "universal" CDM profiles. We find that the more massive clusters are less compact and not as well fit by isothermal spheres as the less massive clusters, possibly indicating that they are still in the process of collapse.Comment: 43 pages, 15 figures, uses aastex, submitted to ApJ 4 color plates produced here as jpg's, larger versions of the jpgs can be found at http://www.mpa-garching.mpg.de/~clow

The first detection of weak gravitational shear in infrared observations: Abell 1689

We present the first detection of weak gravitational shear at infrared wavelengths, using observations of the lensing cluster Abell 1689, taken with the SofI camera on the ESO-NTT telescope. The imprint of cluster lenses on the shapes of the background galaxy population has previously been harnessed at optical wavelengths, and this gravitational shear signal enables cluster mass distributions to be probed, independent of whether the matter is luminous or dark. At near-infrared wavelengths, the spectrophotometric properties of galaxies facilitate a clean selection of background objects for use in the lensing analysis. A finite-field mass reconstruction and application of the aperture mass (Map) statistic are presented. The probability that the peak of the Map detection S/N~5, arises from a chance alignment of background sources is only ~4.5*10^-7. The velocity dispersion of the best-fit singular isothermal sphere model for the cluster is sigma_1D=1030^{+70}_{-80} km/s, and we find a K-band mass-to-light ratio of ~40 M_solar/L_solar inside a 0.44 Mpc radius

Spectroscopy of the neighboring massive clusters Abell 222 and Abell 223

We present a spectroscopic catalog of the neighboring massive clusters Abell 222 and Abell 223. The catalog contains the positions, redshifts, R magnitudes, V-R color, as well as the equivalent widths for a number of lines for 183 galaxies, 153 of them belonging to the A 222 and A 223 system. We determine the heliocentric redshifts to be z=0.2126+/-0.0008 for A 222 and z=0.2079+/-0.0008 for A 223. The velocity dispersions of both clusters in the cluster restframe are about the same: sigma = 1014^{+90}_{-71} km/s and sigma = 1032^{+99}_{-76} km/s for A 222 and A 223, respectively. While we find evidence for substructure in the spatial distribution of A 223, no kinematic substructure can be detected. From the red cluster sequence identified in a color--magnitude--diagram we determine the luminosity of both clusters and derive mass--to--light ratios in the R--band of (M/L)_A222 = (202+/-43) h_70 M_{su}n/L_{sun} and (M/L)_A223 = (149+/-33) h_70 M_{sun}/L_{sun}. Additionally we identify a group of background galaxies at z ~ 0.242.Comment: Accepted for publication in A&A, 10 pages, 9 figures, full version of table 2 included in source distribution, version with higher quality images available from http://www.astro.uni-bonn.de/~dietrich

Gravitational instability on the brane: the role of boundary conditions

An outstanding issue in braneworld theory concerns the setting up of proper boundary conditions for the brane-bulk system. Boundary conditions (BC's) employing regulatory branes or demanding that the bulk metric be nonsingular have yet to be implemented in full generality. In this paper, we take a different route and specify boundary conditions directly on the brane thereby arriving at a local and closed system of equations (on the brane). We consider a one-parameter family of boundary conditions involving the anisotropic stress of the projection of the bulk Weyl tensor on the brane and derive an exact system of equations describing scalar cosmological perturbations on a generic braneworld with induced gravity. Depending upon our choice of boundary conditions, perturbations on the brane either grow moderately (region of stability) or rapidly (instability). In the instability region, the evolution of perturbations usually depends upon the scale: small scale perturbations grow much more rapidly than those on larger scales. This instability is caused by a peculiar gravitational interaction between dark radiation and matter on the brane. Generalizing the boundary conditions obtained by Koyama and Maartens, we find for the Dvali-Gabadadze-Porrati model an instability, which leads to a dramatic scale-dependence of the evolution of density perturbations in matter and dark radiation. A different set of BC's, however, leads to a more moderate and scale-independent growth of perturbations. For the mimicry braneworld, which expands like LCDM, this class of BC's can lead to an earlier epoch of structure formation.Comment: 35 pages, 9 figures, an appendix and references added, version to be published in Classical and Quantum Gravit