Publications (141)544.68 Total impact
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ABSTRACT: We investigate the impact of astrophysical systematics on cosmic shear cosmological parameter constraints from the CanadaFranceHawaii Telescope Lensing Survey (CFHTLenS), and the concordance with cosmic microwave background measurements by Planck. We present updated CFHTLenS cosmic shear tomography measurements extended to degree scales using a covariance calibrated by a new suite of Nbody simulations. We analyze these measurements with a new model fitting pipeline, accounting for key systematic uncertainties arising from intrinsic galaxy alignments, baryonic effects in the nonlinear matter power spectrum, and photometric redshift uncertainties. We examine the impact of the systematic degrees of freedom on the cosmological parameter constraints, both independently and jointly. When the systematic uncertainties are considered independently, the intrinsic alignment amplitude is the only degree of freedom that is substantially preferred by the data. When the systematic uncertainties are considered jointly, there is no consistently strong preference in favor of the more complex models. We quantify the level of concordance between the CFHTLenS and Planck datasets by employing two distinct data concordance tests, grounded in Bayesian evidence and information theory. We find that the two data concordance tests largely agree with one another, and that the level of concordance between the CFHTLenS and Planck datasets is sensitive to the exact details of the systematic uncertainties included in our analysis, ranging from decisive discordance to substantial concordance as the treatment of the systematic uncertainties becomes more conservative. The least conservative scenario is the one most favored by the cosmic shear data, but it is also the one that shows the greatest degree of discordance with Planck. The data and analysis code are public at https://github.com/sjoudaki/cfhtlens_revisited 
Article: Cluster mass profile reconstruction with size and flux magnification on the HST STAGES survey
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ABSTRACT: We present the first measurement of individual cluster mass estimates using weak lensing size and flux magnification. Using data from the HST STAGES (Space Telescope A901/902 Galaxy Evolution Survey) survey of the A901/902 supercluster we detect the four known groups in the supercluster at high significance using magnification alone. We discuss the application of a fully Bayesian inference analysis, and investigate a broad range of potential systematics in the application of the method. We compare our results to a previous weak lensing shear analysis of the same field finding the recovered signaltonoise of our magnificationonly analysis to range from 45 to 110 per cent of the signaltonoise in the shearonly analysis. On a casebycase basis we find consistent magnification and shear constraints on cluster virial radius, and finding that for the full sample, magnification constraints to be a factor 0.77 ± 0.18 lower than the shear measurements.  [Show abstract] [Hide abstract]
ABSTRACT: We present a reanalysis of the CFHTLenS weak gravitational lensing survey using Complete Orthogonal Sets of E/Bmode Integrals, known as COSEBIs. COSEBIs provide a complete set of functions to efficiently separate Emodes from Bmodes and hence allow for robust and stringent tests for systematic errors in the data. This analysis reveals significant Bmodes on large angular scales that were not previously seen using the standard E/B decomposition analyses. We find that the significance of the Bmodes is enhanced when the data is split by galaxy type and analysed in tomographic redshift bins. Adding tomographic bins to the analysis increases the number of COSEBIs modes, which results in a less accurate estimation of the covariance matrix from a set of simulations. We therefore also present the first compressed COSEBIs analysis of survey data, where the COSEBIs modes are optimally combined based on their sensitivity to cosmological parameters. In this tomographic CCOSEBIs analysis we find the Bmodes to be consistent with zero when the full range of angular scales are considered.  [Show abstract] [Hide abstract]
ABSTRACT: We determine the accuracy of galaxy redshift distributions as estimated from photometric redshift probability distributions $p(z)$. Our method utilises measurements of the angular crosscorrelation between photometric galaxies and an overlapping sample of galaxies with spectroscopic redshifts. We describe the redshift leakage from a galaxy photometric redshift bin $j$ into a spectroscopic redshift bin $i$ using the sum of the $p(z)$ for the galaxies residing in bin $j$. We can then predict the angular crosscorrelation between photometric and spectroscopic galaxies due to intrinsic galaxy clustering when $i \neq j$ as a function of the measured angular crosscorrelation when $i=j$. We also account for enhanced clustering arising from lensing magnification using a halo model. The comparison of this prediction with the measured signal provides a consistency check on the validity of using the summed $p(z)$ to determine galaxy redshift distributions in cosmological analyses, as advocated by the CanadaFranceHawaii Telescope Lensing Survey (CFHTLenS). We present an analysis of the photometric redshifts measured by CFHTLenS, which overlaps the Baryon Oscillation Spectroscopic Survey (BOSS). We also analyse the Redsequence Cluster Lensing Survey (RCSLenS), which overlaps both BOSS and the WiggleZ Dark Energy Survey. We find that the summed $p(z)$ from both surveys are generally biased with respect to the true underlying distributions. If unaccounted for, this bias would lead to errors in cosmological parameter estimation from CFHTLenS by less than $\sim 4\%$. For photometric redshift bins which spatially overlap in 3D with our spectroscopic sample, we determine redshift bias corrections which can be used in future cosmological analyses that rely on accurate galaxy redshift distributions.  [Show abstract] [Hide abstract]
ABSTRACT: We present measurements of the galaxy bias b and the galaxy–matter crosscorrelation coefficient r for the Baryon Oscillation Spectroscopic Survey LOWZ luminous red galaxy sample. Using a new statistical weak lensing analysis of the Red Cluster Sequence Lensing Survey (RCSLenS), we find the bias properties of this sample to be higher than previously reported with $b=2.45_{0.05}^{+0.05}$ and $r=1.64_{0.16}^{+0.17}$ on scales between 3 and 20 arcmin. We repeat the measurement for angular scales of 20 arcmin ≤ ϑ ≤ 70 arcmin, which yields $b=2.39_{0.07}^{+0.07}$ and $r=1.24_{0.25}^{+0.26}$. This is the first application of a data compression analysis using a complete set of discrete estimators for galaxy–galaxy lensing and galaxy clustering. As cosmological data sets grow, our new method of data compression will become increasingly important in order to interpret joint weak lensing and galaxy clustering measurements and to estimate the data covariance. In future studies, this formalism can be used as a tool to study the largescale structure of the Universe to yield a precise determination of cosmological parameters.  [Show abstract] [Hide abstract]
ABSTRACT: In this paper we present results of applying the shearratio method to the RCSLenS data. The method takes the ratio of the mean of the weak lensing tangential shear signal about galaxy clusters, averaged over all clusters of the same redshift, in multiple background redshift bins. In taking a ratio the massdependency of the shear signal is cancelledout leaving a statistic that is dependent on the geometric part of the lensing kernel only. We apply this method to 535 clusters and measure a cosmologyindependent distanceredshift relation to redshifts z~1. In combination with Planck data the method lifts the degeneracies in the CMB measurements, resulting in cosmological parameter constraints of OmegaM=0.31 +/ 0.10 and w0 = 1.02 +/ 0.37, for a flat wCDM cosmology.  [Show abstract] [Hide abstract]
ABSTRACT: We present a complete derivation of the observationally motivated definition of the modified gravity statistic $E_G$. Using this expression, we investigate how variations to theory and survey parameters may introduce uncertainty in the general relativistic prediction of $E_G$. We forecast errors on $E_G$ for measurements using two combinations of upcoming surveys, and find that theoretical uncertainties may dominate for a futuristic measurement. Finally, we compute predictions of $E_G$ under modifications to general relativity in the quasistatic regime, and comment on the pros and cons of using $E_G$ to test gravity with future surveys.  [Show abstract] [Hide abstract]
ABSTRACT: Applying a transformation to a nonGaussian field can enhance the information content of the resulting power spectrum, by reducing the correlations between Fourier modes. In the context of weak gravitational lensing, it has been shown that this gain in information content is significantly compromised by the presence of shape noise. We apply clipping to mock convergence fields, a technique which is known to be robust in the presence of noise and has been successfully applied to galaxy number density fields. When analysed in isolation the resulting convergence power spectrum returns degraded constraints on cosmological parameters. However, substantial gains can be achieved by performing a combined analysis of the power spectra derived from both the original and transformed fields. Even in the presence of realistic levels of shape noise, we demonstrate that this approach is capable of reducing the area of likelihood contours within the Ωm − σ8 plane by more than a factor of 3.  [Show abstract] [Hide abstract]
ABSTRACT: We present weak lensing constraints on the ellipticity of galaxyscale matter haloes and the galaxyhalo misalignment. Using data from the Canada–France–Hawaii Telescope Lensing Survey (CFHTLenS), we measure the weightedaverage ratio of the aligned projected ellipticity components of galaxy matter haloes and their embedded galaxies, fh, split by galaxy type. We then compare our observations to measurements taken from the Millennium Simulation, assuming different models of galaxyhalo misalignment. Using the Millennium Simulation, we verify that the statistical estimator used removes contamination from cosmic shear. We also detect an additional signal in the simulation, which we interpret as the impact of intrinsic shape–shear alignments between the lenses and their largescale structure environment. These alignments are likely to have caused some of the previous observational constraints on fh to be biased high. From CFHTLenS, we find fh = −0.04 ± 0.25 for earlytype galaxies, which is consistent with current models for the galaxyhalo misalignment predicting fh ≃ 0.20. For latetype galaxies we measure $f_\mathrm{h}=0.69_{0.36}^{+0.37}$ from CFHTLenS. This can be compared to the simulated results which yield fh ≃ 0.02 for misaligned latetype models.  [Show abstract] [Hide abstract]
ABSTRACT: The unknown nature of ‘dark energy’ motivates continued cosmological tests of largescale gravitational physics. We present a new consistency check based on the relative amplitude of nonrelativistic galaxy peculiar motions, measured via redshiftspace distortion, and the relativistic deflection of light by those same galaxies traced by galaxy–galaxy lensing. We take advantage of the latest generation of deep, overlapping imaging and spectroscopic data sets, combining the Red Cluster Sequence Lensing Survey, the Canada–France–Hawaii Telescope Lensing Survey, the WiggleZ Dark Energy Survey and the Baryon Oscillation Spectroscopic Survey. We quantify the results using the ‘gravitational slip’ statistic EG, which we estimate as 0.48 ± 0.10 at z = 0.32 and 0.30 ± 0.07 at z = 0.57, the latter constituting the highest redshift at which this quantity has been determined. These measurements are consistent with the predictions of General Relativity, for a perturbed Friedmann–Robertson–Walker metric in a Universe dominated by a cosmological constant, which are EG = 0.41 and 0.36 at these respective redshifts. The combination of redshiftspace distortion and gravitational lensing data from current and future galaxy surveys will offer increasingly stringent tests of fundamental cosmology. 
Article: The masses of satellites in GAMA galaxy groups from 100 square degrees of KiDS weak lensing data
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ABSTRACT: We use the first 100 deg2 of overlap between the KiloDegree Survey and the Galaxy And Mass Assembly survey to determine the average galaxy halo mass of ∼10 000 spectroscopically confirmed satellite galaxies in massive (M > 1013 h−1 M⊙) galaxy groups. Separating the sample as a function of projected distance to the group centre, we jointly model the satellites and their host groups with Navarro–Frenk–White density profiles, fully accounting for the data covariance. The probed satellite galaxies in these groups have total masses log 〈Msub/(h−1 M⊙)〉 ≈ 11.7–12.2 consistent across groupcentric distance within the errorbars. Given their typical stellar masses, log 〈M⋆, sat/(h−2 M⊙)〉 ∼ 10.5, such total masses imply stellar mass fractions of 〈M⋆, sat〉/〈Msub〉 ≈ 0.04 h−1. The average subhalo hosting these satellite galaxies has a mass Msub ∼ 0.015Mhost independent of host halo mass, in broad agreement with the expectations of structure formation in a Λ cold dark matter universe. 
Article: Dark matter halo properties of GAMA galaxy groups from 100 square degrees of KiDS weak lensing data
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ABSTRACT: The KiloDegree Survey is an optical widefield survey designed to map the matter distribution in the Universe using weak gravitational lensing. In this paper, we use these data to measure the density profiles and masses of a sample of ∼1400 spectroscopically identified galaxy groups and clusters from the Galaxy And Mass Assembly survey. We detect a highly significant signal (signaltonoiseratio ∼120), allowing us to study the properties of dark matter haloes over one and a half order of magnitude in mass, from M ∼ 1013–1014.5 h−1 M⊙. We interpret the results for various subsamples of groups using a halo model framework which accounts for the miscentring of the brightest cluster galaxy (used as the tracer of the group centre) with respect to the centre of the group's dark matter halo. We find that the density profiles of the haloes are well described by an NFW profile with concentrations that agree with predictions from numerical simulations. In addition, we constrain scaling relations between the mass and a number of observable group properties. We find that the mass scales with the total rband luminosity as a power law with slope 1.16 ± 0.13 (1σ) and with the group velocity dispersion as a power law with slope 1.89 ± 0.27 (1σ). Finally, we demonstrate the potential of weak lensing studies of groups to discriminate between models of baryonic feedback at group scales by comparing our results with the predictions from the CosmoOverWhelmingly Large Simulations project, ruling out models without AGN feedback.  [Show abstract] [Hide abstract]
ABSTRACT: The KiloDegree Survey (KiDS) is a multiband imaging survey designed for cosmological studies from weak lensing and photometric redshifts. It uses the ESO VLT Survey Telescope with its widefield camera OmegaCAM. KiDS images are taken in four filters similar to the SDSS ugri bands. The bestseeing time is reserved for deep rband observations that reach a median 5sigma limiting AB magnitude of 24.9 with a median seeing that is better than 0.7arcsec. Initial KiDS observations have concentrated on the GAMA regions near the celestial equator, where extensive, highly complete redshift catalogues are available. A total of 101 survey tiles, one square degree each, form the basis of the first set of lensing analyses, which focus on measurements of halo properties of GAMA galaxies. 9 galaxies per square arcminute enter the lensing analysis, for an effective inverse shear variance of 69 per square arcminute. Accounting for the shape measurement weight, the median redshift of the sources is 0.53. KiDS data processing follows two parallel tracks, one optimized for galaxy shape measurement (for weak lensing), and one for accurate matchedaperture photometry in four bands (for photometric redshifts). This technical paper describes how the lensing and photometric redshift catalogues have been produced (including an extensive description of the Gaussian Aperture and Photometry pipeline), summarizes the data quality, and presents extensive tests for systematic errors that might affect the lensing analyses. We also provide first demonstrations of the suitability of the data for cosmological measurements, and explain how the shear catalogues were blinded to prevent confirmation bias in the scientific analyses. The KiDS shear and photometric redshift catalogues, presented in this paper, are released to the community through http://kids.strw.leidenuniv.nl .  [Show abstract] [Hide abstract]
ABSTRACT: The KiloDegree Survey (KiDS) is an optical widefield imaging survey carried out with the VLT Survey Telescope and the OmegaCAM camera. KiDS will image 1500 square degrees in four filters (ugri), and together with its nearinfrared counterpart VIKING will produce deep photometry in nine bands. Designed for weak lensing shape and photometric redshift measurements, the core science driver of the survey is mapping the largescale matter distribution in the Universe back to a redshift of ~0.5. Secondary science cases are manifold, covering topics such as galaxy evolution, Milky Way structure, and the detection of highredshift clusters and quasars. KiDS is an ESO Public Survey and dedicated to serving the astronomical community with highquality data products derived from the survey data, as well as with calibration data. Public data releases will be made on a yearly basis, the first two of which are presented here. For a total of 148 survey tiles (~160 sq.deg.) astrometrically and photometrically calibrated, coadded ugri images have been released, accompanied by weight maps, masks, source lists, and a multiband source catalog. A dedicated pipeline and data management system based on the AstroWISE software system, combined with newly developed masking and source classification software, is used for the data production of the data products described here. The achieved data quality and early science projects based on the data products in the first two data releases are reviewed in order to validate the survey data. Early scientific results include the detection of nine highz QSOs, fifteen candidate strong gravitational lenses, highquality photometric redshifts and galaxy structural parameters for hundreds of thousands of galaxies. (Abridged)  [Show abstract] [Hide abstract]
ABSTRACT: We present an optimized variant of the halo model, designed to produce accurate matter power spectra well into the nonlinear regime for a wide range of cosmological models. To do this, we introduce physically motivated free parameters into the halomodel formalism and fit these to data from highresolution Nbody simulations. For a variety of Λ cold dark matter (ΛCDM) and wCDM models, the halomodel power is accurate to ≃ 5 per cent for k ≤ 10h Mpc−1 and z ≤ 2. An advantage of our new halo model is that it can be adapted to account for the effects of baryonic feedback on the power spectrum. We demonstrate this by fitting the halo model to power spectra from the OWLS (OverWhelmingly Large Simulations) hydrodynamical simulation suite via parameters that govern halo internal structure. We are able to fit all feedback models investigated at the 5 per cent level using only two free parameters, and we place limits on the range of these halo parameters for feedback models investigated by the OWLS simulations. Accurate predictions to high k are vital for weaklensing surveys, and these halo parameters could be considered nuisance parameters to marginalize over in future analyses to mitigate uncertainty regarding the details of feedback. Finally, we investigate how lensing observables predicted by our model compare to those from simulations and from halofit for a range of kcuts and feedback models and quantify the angular scales at which these effects become important. Code to calculate power spectra from the model presented in this paper can be found at https://github.com/alexandermead/hmcode.  [Show abstract] [Hide abstract]
ABSTRACT: We present the first cosmological measurement derived from a galaxy density field subject to a `clipping' transformation. By enforcing an upper bound on the galaxy number density field in the Galaxy and Mass Assembly survey (GAMA), contributions from the nonlinear processes of virialisation and galaxy bias are greatly reduced. This leads to a galaxy power spectrum which is easier to model, without calibration from numerical simulations. We develop a theoretical model for the power spectrum of a clipped field in redshift space, which is exact for the case of anisotropic Gaussian fields. Clipping is found to extend the applicability of the conventional Kaiser prescription by more than a factor of three in wavenumber, or a factor of thirty in terms of the number of Fourier modes. By modelling the galaxy power spectrum on scales k < 0.3 h/Mpc and density fluctuations $\delta_g < 4$ we measure the normalised growth rate $f\sigma_8(z = 0.18) = 0.29 \pm 0.10$.  [Show abstract] [Hide abstract]
ABSTRACT: Aims. We present the detection, identification and calibration of extended sources in the deepest Xray dataset to date, the Extended Chandra Deep Field South (ECDFS). Methods. Ultradeep observations of ECDFS with Chandra and XMMNewton enable a search for extended Xray emission down to an unprecedented flux of 2 × 10^(16) ergs s^(1) cm^(2). By using simulations and comparing them with the Chandra and XMM data, we show that it is feasible to probe extended sources of this flux level, which is 10 000 times fainter than the first Xray group catalogs of the ROSAT all sky survey. Extensive spectroscopic surveys at the VLT and Magellan have been completed, providing spectroscopic identification of galaxy groups to high redshifts. Furthermore, available HST imaging enables a weaklensing calibration of the group masses. Results. We present the search for the extended emission on spatial scales of 32′′ in both Chandra and XMM data, covering 0.3 square degrees and model the extended emission on scales of arcminutes. We present a catalog of 46 spectroscopically identified groups, reaching a redshift of 1.6. We show that the statistical properties of ECDFS, such as log N − log S and Xray luminosity function are broadly consistent with LCDM, with the exception that dn/dz/dΩ test reveals that a redshift range of 0.2 < z < 0.5 in ECDFS is sparsely populated. The lack of nearby structure, however, makes studies of highredshift groups particularly easier both in Xrays and lensing, due to a lower level of clustered foreground. We present one and two point statistics of the galaxy groups as well as weaklensing analysis to show that the detected lowluminosity systems are indeed lowmass systems. We verify the applicability of the scaling relations between the Xray luminosity and the total mass of the group, derived for the COSMOS survey to lower masses and higher redshifts probed by ECDFS by means of stacked weak lensing and clustering analysis, constraining any possible departures to be within 30% in mass. Conclusions. Ultradeep Xray surveys uniquely probe the lowmass galaxy groups across a broad range of redshifts. These groups constitute the most common environment for galaxy evolution. Together with the exquisite data set available in the best studied part of the Universe, the ECDFS group catalog presented here has an exceptional legacy value.  [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.  [Show abstract] [Hide abstract]
ABSTRACT: We study the correlations of the shear signal between triplets of sources in the CanadaFranceHawaii Lensing Survey (CFHTLenS) to probe cosmological parameters via the matter bispectrum. In contrast to previous studies, we adopted a nonGaussian model of the data likelihood which is supported by our simulations of the survey. We find that for stateoftheart surveys, similar to CFHTLenS, a Gaussian likelihood analysis is a reasonable approximation, albeit small differences in the parameter constraints are already visible. For future surveys we expect that a Gaussian model becomes inaccurate. Our algorithm for a refined nonGaussian analysis and data compression is then of great utility especially because it is not much more elaborate if simulated data are available. Applying this algorithm to the thirdorder correlations of shear alone in a blind analysis, we find a good agreement with the standard cosmological model: $\Sigma_8$=$\sigma_8$ $(\Omega_{\rm m}/0.27)^{0.64}$=$0.79^{+0.08}_{0.11}$ for a flat $\Lambda\rm CDM$ cosmology with $h=0.7\pm0.04$ ($68\%$ credible interval). Nevertheless our models provide only moderately good fits as indicated by $\chi^2/{\rm dof}=2.9$, including a $20\%$ r.m.s. uncertainty in the predicted signal amplitude. The models cannot explain a signal drop on scales around 15 arcmin, which may be caused by systematics. It is unclear whether the discrepancy can be fully explained by residual PSF systematics of which we find evidence at least on scales of a few arcmin. Therefore we need a better understanding of higherorder correlations of cosmic shear and their systematics to confidently apply them as cosmological probes.  [Show abstract] [Hide abstract]
ABSTRACT: We present new constraints on the relationship between galaxies and their host dark matter halos, measured from the location of the peak of the stellartohalo mass ratio (SHMR), up to the most massive galaxy clusters at redshift $z\sim0.8$ and over a volume of nearly 0.1~Gpc$^3$. We use a unique combination of deep observations in the CFHTLenS/VIPERS field from the nearUV to the nearIR, supplemented by $\sim60\,000$ secure spectroscopic redshifts, analysing galaxy clustering, galaxygalaxy lensing and the stellar mass function. We interpret our measurements within the halo occupation distribution (HOD) framework, separating the contributions from central and satellite galaxies. We find that the SHMR for the central galaxies peaks at $M_{\rm h, peak} = 1.9^{+0.2}_{0.1}\times10^{12} M_{\odot}$ with an amplitude of $0.025$, which decreases to $\sim0.001$ for massive halos ($M_{\rm h} > 10^{14} M_{\odot}$). Compared to central galaxies only, the total SHMR (including satellites) is boosted by a factor 10 in the highmass regime (clustersize halos), a result consistent with cluster analyses from the literature based on fully independent methods. After properly accounting for differences in modelling, we have compared our results with a large number of results from the literature up to $z=1$: we find good general agreement, independently of the method used, within the typical stellarmass systematic errors at low to intermediate mass (${M}_{\star} < 10^{11} M_{\odot}$) and the statistical errors above. We have also compared our SHMR results to semianalytic simulations and found that the SHMR is tilted compared to our measurements in such a way that they over (under) predict star formation efficiency in central (satellite) galaxies.
Publication Stats
5k  Citations  
544.68  Total Impact Points  
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Institutions

20102015

Scottish Universities Physics Alliance
Glasgow, Scotland, United Kingdom


20002015

The University of Edinburgh
 Institute for Astronomy (IfA)
Edinburgh, Scotland, United Kingdom


2012

The Ohio State University
 Department of Physics
Columbus, Ohio, United States


2009

University of Nottingham
 School of Physics and Astronomy
Nottigham, England, United Kingdom


20062009

University of British Columbia  Vancouver
 Department of Physics and Astronomy
Vancouver, British Columbia, Canada


20072008

Pierre and Marie Curie University  Paris 6
 Institut d'astrophysique de Paris
Paris, IledeFrance, France 
Institut d'astrophysique de Paris
Lutetia Parisorum, ÎledeFrance, France


20042008

Max Planck Institute for Astronomy
Heidelburg, BadenWürttemberg, Germany


20022005

University of Oxford
 Department of Physics
Oxford, England, United Kingdom
