Howard K. C. Yee

Chandra X-Ray Observations of the 0.6 < z < 1.1 Red-Sequence Cluster Survey Sample

We present the results of Chandra observations of 13 optically selected clusters with -->0.6 S/N > 3, although three were not observed long enough to support detailed analysis. Surface brightness profiles are fitted to β models. Integrated spectra are extracted within R2500, and TX and LX information is obtained. We derive gas masses and total masses within R2500 and R500. Cosmologically corrected scaling relations are investigated, and we find the RCS clusters to be consistent with self-similar scaling expectations. However, discrepancies exist between the RCS sample and lower z X-ray-selected samples for relationships involving LX, with the higher z RCS clusters having lower LX for a given TX. In addition, we find that gas mass fractions within R2500 for the high-z RCS sample are lower than expected by a factor of ~2. This suggests that the central entropy of these high-z objects has been elevated by processes such as preheating, mergers, and/or AGN outbursts, that their gas is still infalling, or that they contain comparatively more baryonic matter in the form of stars. Finally, relationships between red-sequence optical richness (Bgc,red

Properties of galaxy dark matter halos from weak lensing

B_{gc ,red }

The WiggleZ Project: AA Omega and dark energy

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A Wide-Field Multi-Wavelength Study of RCS Galaxy Clusters: Tracing Star Formation from the Field to Cluster Cores

t Igt Bt/Igt gc ,red

Galaxy Evolution in Rich Clusters at z>1

-->) and X-ray properties are fitted to the data. For systems with measured TX, we find that optical richness correlates with both TX and mass, having a scatter of ~30% with mass for both X-ray-selected and optically selected clusters. However, we also find that X-ray luminosity is not well correlated with richness and that several of our sample members appear to be significantly X-ray faint.

The SpARCS z > 1 Cluster Survey

We present the results of a study of weak lensing by galaxies based on 45.5 deg2 of RC-band imaging data from the Red-Sequence Cluster Survey (RCS). We define a sample of lenses with 19:5 < RC < 21 and a sample of background galaxies with 21:5 < RC < 24. We present the first weak-lensing detection of the flattening of galaxy dark matter halos. We use a simple model in which the ellipticity of the halo is f times the observed ellipticity of the lens. We find a best-fit value of f 1⁄4 0:77þ0:18 0:21, which suggests that the dark matter halos are somewhat rounder than the light distribution. The fact that we detect a significant flattening implies that the halos are well aligned with the light distribution. Given the average ellipticity of the lenses, this implies a halo ellipticity of hehaloi 1⁄4 0:33þ0:07 0:09, in fair agreement with results from numerical simulations of cold dark matter. We note that this result is formally a lower limit to the flattening, since the measurements imply a larger flattening if the halos are not aligned with the light distribution. Alternative theories of gravity (without dark matter) predict an isotropic lensing signal, which is excluded with 99.5% confidence. Hence, our results provide strong support for the existence of dark matter. We also study the average mass profile around the lenses, using a maximum likelihood analysis. We consider two models for the halo mass profile: a truncated isothermal sphere (TIS) and a Navarro-Frenk-White (NFW) profile. We adopt observationally motivated scaling relations between the lens luminosity and the velocity dispersion and the extent of the halo. The TIS model yields a best-fit velocity dispersion of 1⁄4 136 5 3 km s 1 (all errors are 68% confidence limits; the first error bar indicates the statistical uncertainty, whereas the second error bar indicates the systematic error) and a truncation radius s 1⁄4 185þ30 28 h 1 kpc for a galaxy with a fiducial luminosity of LB 1⁄4 10 h 2 LB; (under the assumption that the luminosity does not evolve with redshift). Alternatively, the best-fit NFW model yields a mass M200 1⁄4 (8:4 0:7 0:4) ; 10 h 1 M and a scale radius rs 1⁄4 16:2þ3:6 2:9 h 1 kpc. This value for the scale radius is in excellent agreement with predictions from numerical simulations for a halo of this mass. Subject headings: cosmology: observations — dark matter — galaxies: halos — gravitational lensing