Publications (181)424.56 Total impact
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ABSTRACT: We derived constraints on cosmological parameters using weak lensing peak statistics measured on the $\sim130~\rm{deg}^2$ of the CanadaFranceHawaii Telescope Stripe82 Survey (CS82). This analysis, based on a fast GPU code, demonstrates the feasibility of using peak statistics in cosmological studies. For our measurements, we considered peaks with signaltonoise ratio in the range of $\nu=[3,6]$. For a flat $\Lambda$CDM model with only $(\Omega_{\rm m}, \sigma_8)$ as free parameters, we constrained the parameters of the following relation $\Sigma_8=\sigma_8(\Omega_{\rm m}/0.27)^{\alpha}$ to be: $\Sigma_8=0.82 \pm 0.03 $ and $\alpha=0.43\pm 0.02$. The $\alpha$ value found is considerably smaller than the one measured in twopoint and threepoint cosmic shear correlation analyses, showing a significant complementarity of peak statistics to standard weak lensing cosmological studies. The derived constraints on $(\Omega_{\rm m}, \sigma_8)$ are fully consistent with the ones from either WMAP9 or current Planck (with a better agreement with WMAP9 results). From the weak lensing peak abundances alone, we obtained marginalised mean values of $\Omega_{\rm m}=0.38^{+0.27}_{0.24}$ and $\sigma_8=0.81^{+0.26}_{0.26}$. Finally, we also explored the potential of using weak lensing peak statistics to constrain the massconcentration relation of dark matter halos simultaneously with cosmological parameters.12/2014;  [Show abstract] [Hide abstract]
ABSTRACT: Finding a sample of the most massive clusters with redshifts $z>0.6$ can provide an interesting consistency check of the $\Lambda$CDM model. Here we present results from our search for clusters with $0.6<z<1.0$ where the initial candidates were selected by crosscorrelating the RASS faint and bright source catalogs with red galaxies from the Sloan Digital Sky Survey DR8. Our survey thus covers $\approx10,000\,\rm{deg^2}$, much larger than previous studies. Deeper followup observations in three bands using the William Herrschel Telescope and the Large Binocular Telescope were performed to confirm the candidates, resulting in a sample of 44 clusters for which we present richnesses and red sequence redshifts, as well as spectroscopic redshifts for a subset. At least two of the clusters in our sample are comparable in richness to RCS2$J$232727.7$$020437, one of the richest systems discovered to date. We also obtained new observations with the Combined Array for Research in Millimeter Astronomy for a subsample of 21 clusters. For eleven of those we detect the SunyaevZel'dovich effect signature. The SunyaevZel'dovich signal allows us to estimate $M_{200}$ and check for tension with the cosmological standard model. We find no tension between our cluster masses and the $\Lambda$CDM model.12/2014;  [Show abstract] [Hide abstract]
ABSTRACT: We describe our cluster detection algorithm RedGOLD, based on the search of redsequence galaxy overdensities. In this work, the algorithm is optimized to search for clusters up to z̃1 using optical data. We applied this algorithm to semianalytic simulations and we found that for haloes more massive than M≥ 10^{14} M_{☉} the completeness is 80% and the purity is ̃81%, up to redshift z=1.11/2014; 
Article: Brightest Xray clusters of galaxies in the CFHTLS wide fields: Catalog and optical mass estimator
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ABSTRACT: The CFHTLS presents a unique data set for weak lensing studies, having high quality imaging and deep multiband photometry. We have initiated an XMMCFHTLS project to provide Xray observations of the brightest Xray selected clusters within the wide CFHTLS area. Performance of these observations and the high quality of CFHTLS data, allows us to revisit the identification of Xray sources, introducing automated reproducible algorithms, based on the multicolor red sequence finder. We have also introduced a new optical mass proxy. We provide the calibration of the red sequence observed in the CFHT filters and compare the results with the traditional single color red sequence and photoz. We test the identification algorithm on the subset of highly significant XMM clusters and identify 100% of the sample. We find that the integrated zband luminosity of the red sequence galaxies correlates well with the Xray luminosity with a surprisingly small scatter of 0.20 dex. We further use the multicolor red sequence to reduce spurious detections in the full XMM and RASS data sets, resulting in catalogs of 196 and 32 clusters, respectively. We made spectroscopic followup observations of some of these systems with HECTOSPEC and in combination with BOSS DR9 data. We also describe the modifications needed to the source detection algorithm in order to keep high purity of extended sources in the shallow Xray data. We also present the scaling relation between Xray luminosity and velocity dispersion.The Astrophysical Journal 11/2014; · 6.28 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We present weak lensing and Xray analysis of 12 low mass clusters from the CFHTLenS and XMMCFHTLS surveys. We combine these systems with highmass systems from CCCP and lowmass systems from COSMOS to obtain a sample of 70 systems, which we divide into subsamples of 15 merging and 55 relaxed systems. We measure LT, ML and MT scaling relations and find in all cases that the powerlaw slopes of the full, merging and relaxed subsamples are consistent. For the MT we find slopes consistent with the selfsimilar model, whereas LT results in steeper and ML in flatter relations. We find a marginal trend for larger scatter and lower normalisation in the ML and MT relations for the merging subsample, which we attribute to triaxiality and substructure. We explore the effects of Xray crosscalibration and find that Chandra calibration leads to flatter LT and MT relations. We also utilise the three surveys making up the sample as overlapping mass bins. For COSMOS and CFHTLS we find slopes consistent with the relation fitted to the full sample, whereas the high mass CCCP sample favours flatter slopes. We also find that intermediate mass systems have a higher mass for their luminosity. Unfortunately our sample does not enable direct measurement of a break at low masses, but we find a trend for enhanced intrinsic scatter in mass at low masses.10/2014;  [Show abstract] [Hide abstract]
ABSTRACT: The Next Generation Virgo Cluster Survey is an optical imaging survey covering 104 deg^2 centered on the Virgo cluster. Currently, the complete survey area has been observed in the u*gizbands and one third in the rband. We present the photometric redshift estimation for the NGVS background sources. After a dedicated data reduction, we perform accurate photometry, with special attention to precise color measurements through point spread functionhomogenization. We then estimate the photometric redshifts with the Le Phare and BPZ codes. We add a new prior which extends to iAB = 12.5 mag. When using the u*grizbands, our photometric redshifts for 15.5 \le i \lesssim 23 mag or zphot \lesssim 1 galaxies have a bias \Delta z < 0.02, less than 5% outliers, and a scatter \sigma_{outl.rej.} and an individual error on zphot that increase with magnitude (from 0.02 to 0.05 and from 0.03 to 0.10, respectively). When using the u*gizbands over the same magnitude and redshift range, the lack of the rband increases the uncertainties in the 0.3 \lesssim zphot \lesssim 0.8 range (0.05 < \Delta z < 0.02, \sigma_{outl.rej} ~ 0.06, 1015% outliers, and zphot.err. ~ 0.15). We also present a joint analysis of the photometric redshift accuracy as a function of redshift and magnitude. We assess the quality of our photometric redshifts by comparison to spectroscopic samples and by verifying that the angular auto and crosscorrelation function w(\theta) of the entire NGVS photometric redshift sample across redshift bins is in agreement with the expectations.10/2014;  [Show abstract] [Hide abstract]
ABSTRACT: We present the cluster massrichness scaling relation calibrated by a weak lensing analysis of >18,000 galaxy cluster candidates in the CanadaFranceHawaii Telescope Lensing Survey (CFHTLenS). Detected using the 3DMatchedFilter clusterfinder of Milkeraitis et al., these cluster candidates span a wide range of masses, from the small group scale up to $\sim10^{15} M_{\odot}$, and redshifts 0.2 $\lesssim z\lesssim$ 0.9. The total significance of the shear measurement amounts to 54$\sigma$. We compare cluster masses determined using weak lensing shear and magnification, finding the measurements in individual richness bins to yield 1$\sigma$ compatibility, but with magnification estimates biased low. This first direct mass comparison yields important insights for improving the systematics handling of future lensing magnification work. In addition, we confirm analyses that suggest cluster miscentring has an important effect on the observed 3DMatchedFilter halo profiles, and we quantify this by fitting for projected cluster centroid offsets, which are typically $\sim$ 0.4 arcmin. We bin the cluster candidates as a function of redshift, finding similar cluster masses and richness across the full range up to $z \sim$ 0.9. We measure the 3DMF massrichness scaling relation $M_{200 } = M_0 (N_{200} / 20)^\beta$. We find a normalization $M_0 \sim (2.7^{+0.5}_{0.4}) \times 10^{13} M_{\odot}$, and a logarithmic slope of $\beta \sim 1.4 \pm 0.1$, both of which are in 1$\sigma$ agreement with results from the magnification analysis. We find no evidence for a redshiftdependence of the normalization. The CFHTLenS 3DMatchedFilter cluster catalogue is now available at cfhtlens.org.Monthly Notices of the Royal Astronomical Society 09/2014; 447(2). · 5.23 Impact Factor 
Article: Weak lensing mass map and peak statistics in CanadaFranceHawaii Telescope Stripe 82 survey
Monthly Notices of the Royal Astronomical Society 06/2014; 442(3):25342542. · 5.23 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We present a catalog of 129 Xray galaxy groups, covering a redshift range 0.04<z<1.23, selected in the ~3 square degree part of the CFHTLS W1 field overlapping XMM observations performed under the XMMLSS project. We carry out a statistical study of the redshift evolution out to redshift one of the magnitude gap between the first and the second brightest cluster galaxies of a well defined massselected group sample. We find that the slope of the relation between the fraction of groups and the magnitude gap steepens with redshift, indicating a larger fraction of fossil groups at lower redshifts. We find that 22.2$\pm$6% of our groups at z$\leq$0.6 are fossil groups. We compare our results with the predictions of three semianalytic models based on the Millennium simulation. The intercept of the relation between the magnitude of the brightest galaxy and the value of magnitude gap becomes brighter with increasing redshift. This trend is steeper than the model predictions which we attribute to the younger stellar age of the observed brightest cluster galaxies. This trend argues in favor of stronger evolution of the feedback from active galactic nuclei at z<1 compared to the models. The slope of the relation between the magnitude of the brightest cluster galaxy and the value of the gap does not evolve with redshift and is well reproduced by the models, indicating that the tidal galaxy stripping, put forward as an explanation of the occurrence of the magnitude gap, is both a dominant mechanism and is sufficiently well modeled.Astronomy and Astrophysics 05/2014; 566. · 4.48 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We present a catalog of 129 Xray galaxy groups, covering a redshift range 0.0404/2014;  [Show abstract] [Hide abstract]
ABSTRACT: Higherorder, nonGaussian aspects of the largescale structure carry valuable information on structure formation and cosmology, which is complementary to secondorder statistics. In this work we measure second and thirdorder weaklensing aperturemass moments from CFHTLenS and combine those with CMB anisotropy probes. The third moment is measured with a significance of $2\sigma$. The combined constraint on $\Sigma_8 = \sigma_8 (\Omega_{\rm m}/0.27)^\alpha$ is improved by 10%, in comparison to the secondorder only, and the allowed ranges for $\Omega_{\rm m}$ and $\sigma_8$ are substantially reduced. Including general triangles of the lensing bispectrum yields tighter constraints compared to probing mainly equilateral triangles. Second and thirdorder CFHTLenS lensing measurements improve Planck CMB constraints on $\Omega_{\rm m}$ and $\sigma_8$ by 26% for flat $\Lambda$CDM. For a model with free curvature, the joint CFHTLenSPlanck result is $\Omega_{\rm m} = 0.28 \pm 0.02$ (68% confidence), which is an improvement of 43% compared to Planck alone. We test how our results are potentially subject to three astrophysical sources of contamination: sourcelens clustering, the intrinsic alignment of galaxy shapes, and baryonic effects. We explore future limitations of the cosmological use of thirdorder weak lensing, such as the nonlinear model and the Gaussianity of the likelihood function.Monthly Notices of the Royal Astronomical Society 04/2014; 441(3). · 5.23 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Scaling properties of galaxy cluster observables with mass provide central insights into the processes shaping clusters. Calibrating proxies for cluster mass will be crucial to cluster cosmology with upcoming surveys like eROSITA and Euclid. The recent Planck results led to suggestions that Xray masses might be biased low by $\sim\!40$ %, more than previously considered. We extend the direct calibration of the weak lensing  Xray mass scaling towards lower masses (as low as $1\!\times\!10^{14}\,\mathrm{M}_{\odot}$) in a sample representative of the $z\!\sim\!0.4$$0.5$ population. We investigate the scaling of MMT/Megacam weak lensing (WL) masses for $8$ clusters at $0.39\!\leq\!z\!\leq\!0.80$ as part of the \emph{400d} WL programme with hydrostatic \textit{Chandra} Xray masses as well as those based on the proxies, e.g. $Y_{\mathrm{X}}\!=\!T_{\mathrm{X}}M_{\mathrm{gas}}$. Overall, we find good agreement between WL and Xray masses, with different mass bias estimators all consistent with zero. Subdividing the sample, we find the highmass subsample to show no significant mass bias while for the lowmass subsample, there is a bias towards overestimated Xray masses at the $\sim\!2\sigma$ level for some mass proxies. The overall scatter in the massmass scaling relations is surprisingly low. Neither observation can be traced back to the parameter settings in the WL analysis. We do not find evidence for a strong ($\sim\!40$ %) underestimate in the Xray masses, as suggested to reconcile Planck cluster counts and cosmological constraints. For highmass clusters, our measurements are consistent with studies in the literature. The mass dependent bias, significant at $\sim\!2\sigma$, may hint at a physically different cluster population (less relaxed clusters with more substructure and mergers); or it may be due to small number statistics.02/2014;  [Show abstract] [Hide abstract]
ABSTRACT: This paper presents the first application of 3D cosmic shear to a widefield weak lensing survey. 3D cosmic shear is a technique that analyses weak lensing in three dimensions using a spherical harmonic approach, and does not bin data in the redshift direction. This is applied to CFHTLenS, a 154 square degree imaging survey with a median redshift of 0.7 and an effective number density of 11 galaxies per square arcminute usable for weak lensing. To account for survey masks we apply a 3D pseudoCl approach on weak lensing data, and to avoid uncertainties in the highly nonlinear regime, we separately analyse radial wavenumbers k<=1.5h/Mpc and k<=5.0h/Mpc, and angular wavenumbers l~4005000. We show how one can recover 2D and tomographic power spectra from the full 3D cosmic shear power spectra and present a measurement of the 2D cosmic shear power spectrum, and measurements of a set of 2bin and 6bin cosmic shear tomographic power spectra; in doing so we find that using the 3D power in the calculation of such 2D and tomographic power spectra from data naturally accounts for a minimum scale in the matter power spectrum. We use 3D cosmic shear to constrain cosmologies with parameters OmegaM, OmegaB, sigma8, h, ns, w0, wa. For a nonevolving dark energy equation of state, and assuming a flat cosmology, lensing combined with WMAP7 results in h=0.78+/0.12, OmegaM=0.252+/0.079, sigma8=0.88+/0.23 and w=1.16+/0.38 using only scales k<=1.5h/Mpc. We also present results of lensing combined with first year Planck results, where we find no tension with the results from this analysis, but we also find no significant improvement over the Planck results alone. We find evidence of a suppression of power compared to LCDM on small scales 1.5<k<=5.0h/Mpc in the lensing data, which is consistent with predictions of the effect of baryonic feedback on the matter power spectrum. [abridged]Monthly Notices of the Royal Astronomical Society 01/2014; 442(2). · 5.23 Impact Factor 
Article: First GalaxyGalaxy Lensing Measurement of Satellite Halo Mass in the CFHT/MegaCam Stripe82 Survey
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ABSTRACT: We select satellite galaxies from the galaxy group catalog constructed with the SDSS spectroscopic galaxies and measure the tangential shear around these galaxies with source catalog extracted from CFHT/MegaCam Stripe82 Survey to constrain the mass of subhalos associated with them. The lensing signal is measured around satellites in groups with masses in the range [10^{13}, 5x10^{14}]h^{1}M_{sun}, and is found to agree well with theoretical expectation. Fitting the data with a truncated NFW profile, we obtain an average subhalo mass of log M_{sub}= 11.68 \pm 0.67 for satellites whose projected distances to central galaxies are in the range [0.1, 0.3] h^{1}Mpc, and log M_{sub}= 11.68 \pm 0.76 for satellites with projected halocentric distance in [0.3, 0.5] h^{1}Mpc. The bestfit subhalo masses are comparable to the truncated subhalo masses assigned to satellite galaxies using abundance matching and about 5 to 10 times higher than the average stellar mass of the lensing satellite galaxies.Monthly Notices of the Royal Astronomical Society 11/2013; · 5.23 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We measure the crosscorrelation of cosmic microwave background lensing convergence maps derived from Atacama Cosmology Telescope data with galaxy lensing convergence maps as measured by the CanadaFranceHawaii Telescope Stripe 82 Survey. The CMBgalaxy lensing cross power spectrum is measured for the first time with a significance of 3.2{\sigma}, which corresponds to a 16% constraint on the amplitude of density fluctuations at redshifts ~ 0.9. With upcoming improved lensing data, this novel type of measurement will become a powerful cosmological probe, providing a precise measurement of the mass distribution at intermediate redshifts and serving as a calibrator for systematic biases in weak lensing measurements.11/2013;  [Show abstract] [Hide abstract]
ABSTRACT: We present the weak lensing mass map of the 173 tiles CanadaFranceHawaii Telescope Stripe82 Survey (CS82) with the effective area ~124 square degrees and study the peak statistics, including peak abundance, correlation functions and tangentialshear profile of peaks with the mass map. We find that (1) peak abundance detected in CS82 are consistent with predictions from a LambdaCDM cosmological model, once noise effects are properly included; (2) correlation function of peaks with different signaltonoise ratio (SNR) can be well fitted with power laws. Combining with the SDSSIII/Constant Mass (CMASS) galaxies, the crosscorrelation between CMASS galaxies and high SNR peaks can be wellfitted with a power law; (3) the tangential shear profiles of the peaks increase with SNR. We concentrate on fitting spherical models to the tangential profiles with both singular isothermal sphere (SIS) and Navarro Frenk & White (NFW) models. For the high SNR peaks, the SIS model is rejected at ~3sigma. Comparing the Dark and matched clumps to the optically selected redMaPPer clusters, a difference in lensing signal of a factor of 2 can be found, reflecting the fact that likely about half of the dark clumps are false detection.11/2013;  [Show abstract] [Hide abstract]
ABSTRACT: Galaxygalaxy weak lensing is a direct probe of the mean matter distribution around galaxies. The depth and sky coverage of the CFHT Legacy Survey yield statistically significant galaxy halo mass measurements over a much wider range of stellar masses ($10^{8.75}$ to $10^{11.3} M_{\odot}$) and redshifts ($0.2 < z < 0.8$) than previous weak lensing studies. The stellartohalo mass ratio (SHMR) reaches a maximum of $3.4\pm0.2$ percent as a function of halo mass at $\sim 10^{12.25} M_{\odot}$ (at redshift $z =0.5$). We find, for the first time from weak lensing alone, evidence for significant evolution in the SHMR: the peak ratio falls as a function of cosmic time from $3.8 \pm 0.3$ percent at $z \sim 0.7$ to $3.0 \pm 0.2$ percent at $z \sim 0.3$, and shifts to lower stellar mass haloes. These evolutionary trends are dominated by red galaxies, and are consistent with a model in which the stellar mass above which star formation is quenched "downsizes" with cosmic time. In contrast, the SHMR of blue, starforming galaxies is well fit by a power law that does not evolve with time. This suggests that blue galaxies form stars at a rate that is balanced with their dark matter accretion in such a way that they evolve along the SHMR. This can be used to constrain the mean star formation rate of the galaxy population over cosmic time.Monthly Notices of the Royal Astronomical Society 10/2013; 447(1). · 5.23 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Gravitational lensing magnification is measured with a significance of 9.7 sigma on a large sample of galaxy clusters in the CanadaFranceHawaii Telescope Lensing Survey (CFHTLenS). This survey covers ~154 deg^2 and contains over 18,000 cluster candidates at redshifts 0.2 <= z <= 0.9, detected using the 3DMatched Filter clusterfinder of Milkeraitis et al. (2010). We fit compositeNFW models to the ensemble, accounting for cluster miscentering, sourcelens redshift overlap, as well as nearby structure (the 2halo term), and recover mass estimates of the cluster dark matter halos in range of ~10^13 M_sun to 2*10^14 M_sun. Cluster richness is measured for the entire sample, and we bin the clusters according to both richness and redshift. A massrichness relation M_200 = M_0 (N_200 / 20)^beta is fit to the measurements. For two different cluster miscentering models we find consistent results for the normalization and slope, M_0 = (2.3 +/ 0.2)*10^13 M_sun, beta = 1.4 +/ 0.1 and M_0 = (2.2 +/ 0.2)*10^13 M_sun, beta = 1.5 +/ 0.1. We find that accounting for the full redshift distribution of lenses and sources is important, since any overlap can have an impact on mass estimates inferred from flux magnification.Monthly Notices of the Royal Astronomical Society 10/2013; 439(4). · 5.23 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The spectroscopy mas achieved with MOS observations taken with NTT/EMMI (ESO/La Silla) in 20070821/22. (1 data file).VizieR Online Data Catalog. 08/2013; 
Article: CFHTLenS: The relation between galaxy dark matter haloes and baryons from weak gravitational lensing
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ABSTRACT: We present a study of the relation between dark matter halo mass and the baryonic content of host galaxies, quantified via luminosity and stellar mass. Our investigation uses 154 deg2 of CanadaFranceHawaii Telescope Lensing Survey (CFHTLenS) lensing and photometric data, obtained from the CFHT Legacy Survey. We employ a galaxygalaxy lensing halo model which allows us to constrain the halo mass and the satellite fraction. Our analysis is limited to lenses at redshifts between 0.2 and 0.4. We express the relationship between halo mass and baryonic observable as a power law. For the luminosityhalo mass relation we find a slope of 1.32+/0.06 and a normalisation of 1.19+0.060.07x10^13 h70^1 Msun for red galaxies, while for blue galaxies the bestfit slope is 1.09+0.200.13 and the normalisation is 0.18+0.040.05x10^13 h70^1 Msun. Similarly, we find a bestfit slope of 1.36+0.060.07 and a normalisation of 1.43+0.110.08x10^13 h70^1 Msun for the stellar masshalo mass relation of red galaxies, while for blue galaxies the corresponding values are 0.98+0.080.07 and 0.84+0.200.16x10^13 h70^1 Msun. For red lenses, the fraction which are satellites tends to decrease with luminosity and stellar mass, with the sample being nearly all satellites for a stellar mass of 2x10^9 h70^2 Msun. The satellite fractions are generally close to zero for blue lenses, irrespective of luminosity or stellar mass. This, together with the shallower relation between halo mass and baryonic tracer, is a direct confirmation from galaxygalaxy lensing that blue galaxies reside in less clustered environments than red galaxies. We also find that the halo model, while matching the lensing signal around red lenses well, is prone to overpredicting the largescale signal for faint and less massive blue lenses. This could be a further indication that these galaxies tend to be more isolated than assumed. [abridged]Monthly Notices of the Royal Astronomical Society 04/2013; · 5.23 Impact Factor
Publication Stats
1k  Citations  
424.56  Total Impact Points  
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Institutions

2003–2014

University of Bonn
 ArgelanderInstitute of Astronomy
Bonn, North RhineWestphalia, Germany


2012

French National Centre for Scientific Research
 Observatoire astronomique de Strasbourg
Lutetia Parisorum, ÎledeFrance, France


2005

IT University of Copenhagen
København, Capital Region, Denmark
