arXiv subjects

Henk Hoekstra

Publications and source records attributed to Henk Hoekstra.

206 records · Page 12Linked to original sources

arXiv2002

Lensing results from the Red-sequence Cluster Survey

We present a variety of weak lensing results based on the ongoing analysis of R_C-band imaging data from the Red-Sequence Cluster Survey (RCS). We briefly discuss the weak lensing signal induced by intervening large scale structure (cosmic shear), and study the properties of the dark matter halos surrounding galaxies with 19.5<R_C<21 (which have a median redshift of z=0.35) using a parametrized mass model for the galaxy mass distribution. This allows us for the first time to constrain the extent of the halos. We find a robust upper limit for the truncation parameter s<470 h^{-1} kpc (99.7% confidence). We also study the biasing properties of these galaxies as a function of scale. We find that both the bias parameter b and the galaxy-mass cross-correlation coefficient r vary with scale (on scales 0.1-6 h^{-1} Mpc). Interestingly, we find that r=0.57^{+0.08}_{-0.07} on scales ~0.5 h^{-1} Mpc.

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arXiv2001

U, B and r band luminosity functions of galaxies in the Coma cluster

We present a deep multi-colour CCD mosaic of the Coma cluster (Abell 1656), covering 5.2 deg^2 in the B and r bands, and 1.3 deg^2 in the U band. This large, homogeneous data set provides a valuable low redshift comparison sample for studies of galaxies in distant clusters. In this paper we present our survey, and study the dependence of the galaxy luminosity function (LF) on passband and radial distance from the cluster centre. The U, B and r band LFs of the complete sample cannot be represented by single Schechter functions. For the central area, r<245 h_{100}^{-1} kpc, we find best-fitting Schechter parameters of M^{*}_U=-18.60^{+0.13}_{-0.18} and α_U=-1.32^{+0.018}_{-0.028}, M^{*}_B=-19.79^{+0.18}_{-0.17} and α_B=-1.37^{+0.024}_{-0.016} and M^{*}_r=-20.87^{+0.12}_{-0.17} and α_r=-1.16^{+0.012}_{-0.019}. The LF becomes steeper at larger radial distance from the cluster centre. The effect is most pronounced in the U band. This result is consistent with the presence of a star forming dwarf population at large distance from the cluster centre, which may be in the process of being accreted by the cluster. The shapes of the LFs of the NGC 4839 group support a scenario in which the group has already passed through the centre.

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arXiv2001

The Red-Sequence Cluster Survey: first lensing results

The Red-Sequence Cluster Survey (RCS) is a 100 deg^2 galaxy cluster survey designed to provide a large sample of optically selected clusters of galaxies with redshifts 0.1<z<1.4. The survey data are also useful for a variety of lensing studies. Several strong lensing clusters have been discovered so far, and follow up observations are underway. In these proceedings we present some of the first results of a weak lensing analysis based on ~24 deg^2 of data. We have detected the lensing signal induced by intervening large scale structure (cosmic shear) at high significance, and find σ_8=0.81^{+0.14}_{-0.19} (95% confidence; for a LCDM cosmology. Another application of these data is the study of the average properties of dark matter halos surrounding galaxies. We study the lensing signal from intermediate redshift galaxies with 19.5<R_C<21 using a parametrized mass model for the galaxy mass distribution. The analysis yields a mass weighted velocity dispersion of 111+-5 km/s. In addition we have constrained for the first time the extent of dark matter halos, and find a robust upper limit for the truncation parameter s<470 h^{-1} kpc (99.7% confidence). The biasing properties of these galaxies as a function of scale are also studied. The RCS data allow us to measure the ratio of the bias parameter b and the galaxy-mass cross-correlation coefficient r. The results are consistent with a scale-independent value of b/r, for which we find b/r=1.05^{+0.12}_{-0.10}.

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arXiv2001

HST large field weak lensing analysis of MS 2053-04: study of the mass distribution and mass-to-light ratio of X-ray selected clusters at 0.22<z<0.83

We have detected the weak lensing signal induced by the cluster of galaxies MS 2053-04 (z=0.58) from a two-colour mosaic of 6 HST WFPC2 images. The best fit singular isothermal sphere model to the observed tangential distortion yields an Einstein radius r_E=6.2"+-1.8", which corresponds to a velocity dispersion of 886^{+121}_{-139} km/s. This result is in good agreement with the observed velocity dispersion of 817+-80 km/s from cluster members. MS 2053 is the third cluster we studied using mosaics of deep WFPC2 images. For all three clusters we find good agreement between dynamical and weak lensing velocity dispersions, in contrast to weak lensing studies based on single WFPC2 pointings on cluster cores. This result demonstrates the importance of wide field data. We have compared the ensemble averaged cluster profile to the predicted NFW profile, and find that a NFW profile can fit the observed lensing signal well. The best fit concentration parameter is found to be 0.79^{+0.44}_{-0.15} (68% confidence) times the predicted value from an open CDM model. The observed mass-to-light ratios of the clusters in our sample evolve with redshift, and are inconsistent with a constant, non-evolving, mass-to-light ratio at the 99% confidence level. The evolution is consistent with the results derived from the evolution of the fundamental plane of early type galaxies. The resulting average mass-to-light ratio for massive clusters at z=0 is found to be 239+-18+-9 M/L_B. (abridged)

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arXiv2001

Measurement of the bias parameter from weak lensing

We have measured the correlation between the lensing signal induced by (dark) matter and number counts of galaxies on scales ranging from 0.15-3.0 h_{50}^{-1} Mpc (which correspond to aperture radii of 1-15 arcminutes). This provides a direct probe of the scale dependence of the ratio of the classical bias parameter b and the galaxy-mass correlation coefficient r. The results presented here are based on 16 deg^2 of R_C band data taken with the CFHT as part of the Red-Sequence Cluster Survey. We used a sample of lens galaxies with 19.5<R_C<21, and a sample of source galaxies with 21.5<R_C<24. The results are consistent with a scale independent value of b/r, which provides valuable constraints on models of galaxy formation on scales that can only be probed through weak lensing. For the currently favored cosmology (Ω_m=0.3, Ω_Λ=0.7) we find b/r=1.05^{+0.12}_{-0.10}, similar to what is found on larger scales (~10 h_{50}^{-1} Mpc) from local dynamical estimates. These results support the hypothesis that light traces mass on scales ranging from 0.15 out to ~10 h_{50}^{-1} Mpc. The accuracy of the measurement will improve significantly in the coming years, enabling us to measure both b and r separately as a function of scale.

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arXiv2001

First weak lensing results from the Red-Sequence Cluster Survey

The Red-Sequence Cluster Survey (RCS) is a 100 square degree galaxy cluster survey designed to provide a large sample of optically selected clusters of galaxies with redshifts 0.1 ^{1/2}= 111+-5 km/s. In addition we have constrained for the first time the extent of dark matter halos, and find a robust upper limit for the truncation parameter s<470 h^{-1} kpc (99.7% confidence). A preliminary analysis also excludes a simple ``prediction'' of lensing according to Modified Newtonian Dynamics (MOND) at high confidence.

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arXiv2001

The effect of distant large scale structure on weak lensing mass estimates

We quantify the uncertainty in weak lensing mass estimates of clusters of galaxies, caused by distant (uncorrelated) large scale structure along the line of sight. We find that the effect is fairly small for deep observations (20<R<26) of massive clusters (sigma=1000 km/s) at intermediate redshifts, where the bulk of the sources are at high redshifts compared to the cluster redshift. If the lensing signal is measured out to 1.5 h_{50}^{-1} Mpc the typical 1sigma relative uncertainty in the mass is about 6%. However, in other situations the induced uncertainty can be larger. For instance, in the case of nearby clusters, such as the Coma cluster, background structures introduce a considerable uncertainty in the mass, limiting the maximum achievable S/N-ratio to \sim 7, even for deep observations. The noise in the cluster mass estimate caused by the large scale structure increases with increasing aperture size, which will also complicate attempts to constrain cluster mass profiles at large distances from the cluster centre. However, the distant large scale structure studied here can be considered an additional (statistical) source of error, and by averaging the results of several clusters the noise is decreased.

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arXiv1999

Mass and mass-to-light ratio of galaxy groups from weak lensing

We have measured for the first time the weak lensing signal due to groups of galaxies. The groups are at intermediate redshifts, and have been identified in the CNOC2 field survey, which was kindly made available by Ray Carlberg and Howard Yee. The ensemble averaged group velocity dispersion, based on a preliminary selection of 59 groups, is found to be sigma= 320^{+46}_{-54} km/s, which is in fair agreement with the dynamical estimate from the spectroscopic redshifts. Under the assumption that mass traces light, we find an average mass-to-light ratio in restframe B of (256\pm84)h Msun/Lsun. Using this result we obtain Omega_m=0.22+-0.09 (Ω_Λ=0).

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