Publications (121)480.17 Total impact

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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.Physical Review D 03/2015; 91:062001. DOI:10.1103/PhysRevD.91.062001 · 4.69 Impact Factor 
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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. 
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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. 
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ABSTRACT: Ultradeep observations of ECDFS with Chandra and XMMNewton enable a search for extended Xray emission down to an unprecedented flux of $2\times10^{16}$ ergs s$^{1}$ cm$^{2}$. We present the search for the extended emission on spatial scales of 32$^{\prime\prime}$ 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 logNlogS and Xray luminosity function are broadly consistent with LCDM, with the exception that dn/dz/d$\Omega$ 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. Abridged. 
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ABSTRACT: We investigate the dependence of the galaxy luminosity function on geometric environment within the Galaxy And Mass Assembly (GAMA) survey. The tidal tensor prescription, based on the Hessian of the pseudogravitational potential, is used to classify the cosmic web and define the geometric environments: for a given smoothing scale, we classify every position of the surveyed region, $0.04<{z}<0.26$, as either a void, a sheet, a filament or a knot. We consider how to choose appropriate thresholds in the eigenvalues of the Hessian in order to partition the galaxies approximately evenly between environments. We find a significant variation in the luminosity function of galaxies between different geometric environments; the normalisation, characterised by $\phi^{*}$ in a Schechter function fit, increases by an order of magnitude from voids to knots. The turnover magnitude, characterised by $M^*$, brightens by approximately $0.5$ mag from voids to knots. However, we show that the observed modulation can be entirely attributed to the indirect localdensity dependence. We therefore find no evidence of a direct influence of the cosmic web on the galaxy luminosity function. 
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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. 
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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). DOI:10.1093/mnras/stu2545 · 5.23 Impact Factor 
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ABSTRACT: (Abridged) The effect of baryonic feedback on the dark matter mass distribution is generally considered to be a nuisance to weak gravitational lensing. Measurements of cosmological parameters are affected as feedback alters the cosmic shear signal on angular scales smaller than a few arcminutes. Recent progress on the numerical modelling of baryon physics has shown that this effect could be so large that, rather than being a nuisance, the effect can be constrained with current weak lensing surveys, hence providing an alternative astrophysical insight on one of the most challenging questions of galaxy formation. In order to perform our analysis, we construct an analytic fitting formula that describes the effect of the baryons on the mass power spectrum. This fitting formula is based on three scenarios of the OWL hydrodynamical simulations. It is specifically calibrated for $z<1.5$, where it models the simulations to an accuracy that is better than $2\%$ for scales $k<10 h\mbox{Mpc}^{1}$ and better than $5\%$ for $10 < k < 100 h\mbox{Mpc}^{1}$. Equipped with this precise tool, this paper presents the first constraint on baryonic feedback models using gravitational lensing data, from the Canada France Hawaii Telescope Lensing Survey (CFHTLenS). In this analysis, we show that the effect of neutrino mass on the mass power spectrum is degenerate with the baryonic feedback at small angular scales and cannot be ignored. Assuming a cosmology precision fixed by WMAP9, we find that a universe with no baryon feedback and massless neutrinos is rejected by the CFHTLenS lensing data with 96\% confidence. Our study shows that ongoing weak gravitational lensing surveys (KiDS, HSC and DES) will offer a unique opportunity to probe the physics of baryons at galactic scales, in addition to the expected constraints on the total neutrino mass. 
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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). DOI:10.1093/mnras/stu754 · 5.23 Impact Factor 
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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). DOI:10.1093/mnras/stu934 · 5.23 Impact Factor 
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ABSTRACT: We outline the prospects for performing pioneering radio weak gravitational lensing analyses using observations from a potential forthcoming JVLA Sky Survey program. A largescale survey with the JVLA can offer interesting and unique opportunities for performing weak lensing studies in the radio band, a field which has until now been the preserve of optical telescopes. In particular, the JVLA has the capacity for large, deep radio surveys with relatively high angular resolution, which are the key characteristics required for a successful weak lensing study. We highlight the potential advantages and unique aspects of performing weak lensing in the radio band. In particular, the inclusion of continuum polarisation information can greatly reduce noise in weak lensing reconstructions and can also remove the effects of intrinsic galaxy alignments, the key astrophysical systematic effect that limits weak lensing at all wavelengths. We identify a VLASS "deep fields" program (total area ~1020 square degs), to be conducted at Lband and with highresolution (Aarray configuration), as the optimal survey strategy from the point of view of weak lensing science. Such a survey will build on the unique strengths of the JVLA and will remain unsurpassed in terms of its combination of resolution and sensitivity until the advent of the Square Kilometre Array. We identify the best fields on the JVLAaccessible sky from the point of view of overlapping with existing deep optical and near infrared data which will provide crucial redshift information and facilitate a host of additional compelling multiwavelength science. 
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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). DOI:10.1093/mnras/stu2367 · 5.23 Impact Factor 
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ABSTRACT: The GRavitational lEnsing Accuracy Testing 3 (GREAT3) challenge is the third in a series of image analysis challenges, with a goal of testing and facilitating the development of methods for analyzing astronomical images that will be used to measure weak gravitational lensing. This measurement requires extremely precise estimation of very small galaxy shape distortions, in the presence of far larger intrinsic galaxy shapes and distortions due to the blurring kernel caused by the atmosphere, telescope optics, and instrumental effects. The GREAT3 challenge is posed to the astronomy, machine learning, and statistics communities, and includes tests of three specific effects that are of immediate relevance to upcoming weak lensing surveys, two of which have never been tested in a community challenge before. These effects include realistically complex galaxy models based on highresolution imaging from space; spatially varying blurring kernel; and combination of multiple different exposures. To facilitate entry by people new to the field, and for use as a diagnostic tool, the simulation software for the challenge is publicly available, though the exact parameters used for the challenge are blinded. Sample scripts to analyze the challenge data using existing methods will also be provided. See http://great3challenge.info and http://great3.projects.phys.ucl.ac.uk/leaderboard/ for more information.The Astrophysical Journal Supplement Series 08/2013; 212(1). DOI:10.1088/00670049/212/1/5 · 14.14 Impact Factor 
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ABSTRACT: In this paper, we motivate the use of galaxy clustering measurements using photometric redshift information, including a contribution from flux magnification, as a probe of cosmology. We present cosmological forecasts when clustering data alone is used, and when clustering is combined with a cosmic shear analysis. We consider two types of clustering analysis: firstly, clustering with only redshift autocorrelations in tomographic redshift bins; secondly, using all available redshift bin correlations. Finally, we consider how inferred cosmological parameters may be biased using each analysis when flux magnification is neglected. Results are presented for a Stage III groundbased survey, and a Stage IV spacebased survey modelled with photometric redshift errors, and values for the slope of the luminosity function inferred from CFHTLenS catalogues. We find that combining clustering information with shear can improve constraints on cosmological parameters, giving an improvement to a Dark Energy Task Forcelike figure of merit by a factor of 1.33 when only autocorrelations in redshift are used for the clustering analysis, rising to 1.52 when crosscorrelations in redshift are also included. The addition of galaxygalaxy lensing gives further improvement, with increases in figure of merit by a factor of 2.82 and 3.7 for each type of clustering analysis respectively. The presence of flux magnification in a clustering analysis does not significantly affect the precision of cosmological constraints when combined with cosmic shear and galaxygalaxy lensing. However if magnification is neglected, inferred cosmological parameter values are biased, with biases in some cosmological parameters larger than statistical errors. (Abridged)Monthly Notices of the Royal Astronomical Society 06/2013; 437(3). DOI:10.1093/mnras/stt2060 · 5.23 Impact Factor 
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ABSTRACT: We present a method for suppressing contributions from higherorder terms in perturbation theory, greatly increasing the amount of information which may be extracted from the matter power spectrum. In an evolved cosmological density field the highest density regions are responsible for the bulk of the nonlinear power. By suitably downweighting these problematic regions we find that the one and twoloop terms are typically reduced in amplitude by ~70 per cent and ~95 per cent respectively, relative to the linear power spectrum. This greatly facilitates modelling the shape of the galaxy power spectrum, potentially increasing the number of useful Fourier modes by more than two orders of magnitude. We provide a demonstration of how this technique allows the galaxy bias and the amplitude of linear matter perturbations sigma_8 to be determined from the power spectrum on conventionally nonlinear scales, 0.1<k<0.7 h/Mpc.Physical review D: Particles and fields 06/2013; 88(8). DOI:10.1103/PhysRevD.88.083510 
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; 437(3). DOI:10.1093/mnras/stt2013 · 5.23 Impact Factor 
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ABSTRACT: We present a quantitative analysis of the largest contiguous maps of projected mass density obtained from gravitational lensing shear. We use data from the 154 deg2 covered by the CanadaFranceHawaii Telescope Lensing Survey. Our study is the first attempt to quantitatively characterize the scientific value of lensing maps, which could serve in the future as a complementary approach to the study of the dark universe with gravitational lensing. We show that mass maps contain unique cosmological information beyond that of traditional twopoints statistical analysis techniques. Using a series of numerical simulations, we first show how, reproducing the CFHTLenS observing conditions, gravitational lensing inversion provides a reliable estimate of the projected matter distribution of large scale structure. We validate our analysis by quantifying the robustness of the maps with various statistical estimators. We then apply the same process to the CFHTLenS data. We find that the 2points correlation function of the projected mass is consistent with the cosmological analysis performed on the shear correlation function discussed in the CFHTLenS companion papers. The maps also lead to a significant measurement of the third order moment of the projected mass, which is in agreement with analytic predictions, and to a marginal detection of the fourth order moment. Tests for residual systematics are found to be consistent with zero for the statistical estimators we used. A new approach for the comparison of the reconstructed mass map to that predicted from the galaxy distribution reveals the existence of giant voids in the dark matter maps as large as 3 degrees on the sky. Our analysis shows that lensing mass maps can be used for new techniques such as peak statistics and the morphological analysis of the projected dark matter distribution.Monthly Notices of the Royal Astronomical Society 03/2013; 433(4). DOI:10.1093/mnras/stt971 · 5.23 Impact Factor 
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ABSTRACT: We present a finelybinned tomographic weak lensing analysis of the CanadaFranceHawaii Telescope Lensing Survey, CFHTLenS, mitigating contamination to the signal from the presence of intrinsic galaxy alignments via the simultaneous fit of a cosmological model and an intrinsic alignment model. CFHTLenS spans 154 square degrees in five optical bands, with accurate shear and photometric redshifts for a galaxy sample with a median redshift of zm =0.70. We estimate the 21 sets of cosmic shear correlation functions associated with six redshift bins, each spanning the angular range of 1.5<theta<35 arcmin. We combine this CFHTLenS data with auxiliary cosmological probes: the cosmic microwave background with data from WMAP7, baryon acoustic oscillations with data from BOSS, and a prior on the Hubble constant from the HST distance ladder. This leads to constraints on the normalisation of the matter power spectrum sigma_8 = 0.799 +/ 0.015 and the matter density parameter Omega_m = 0.271 +/ 0.010 for a flat Lambda CDM cosmology. For a flat wCDM cosmology we constrain the dark energy equation of state parameter w = 1.02 +/ 0.09. We also provide constraints for curved Lambda CDM and wCDM cosmologies. We find the intrinsic alignment contamination to be galaxytype dependent with a significant intrinsic alignment signal found for earlytype galaxies, in contrast to the latetype galaxy sample for which the intrinsic alignment signal is found to be consistent with zero.Monthly Notices of the Royal Astronomical Society 03/2013; 432(3). DOI:10.1093/mnras/stt601 · 5.23 Impact Factor 
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ABSTRACT: We use weak gravitational lensing to analyse the dark matter halos around satellite galaxies in galaxy groups in the CFHTLenS dataset. This dataset is derived from the CFHTLSWide survey, and encompasses 154 sq. deg of highquality shape data. Using the photometric redshifts, we divide the sample of lens galaxies with stellar masses in the range 10^9 Msun to 10^10.5 Msun into those likely to lie in highdensity environments (HDE) and those likely to lie in lowdensity environments (LDE). Through comparison with galaxy catalogues extracted from the Millennium Simulation, we show that the sample of HDE galaxies should primarily (~61%) consist of satellite galaxies in groups, while the sample of LDE galaxies should consist of mostly (~87%) nonsatellite (field and central) galaxies. Comparing the lensing signals around samples of HDE and LDE galaxies matched in stellar mass, the lensing signal around HDE galaxies clearly shows a positive contribution from their host groups on their lensing signals at radii of ~5001000 kpc, the typical separation between satellites and group centres. More importantly, the subhalos of HDE galaxies are less massive than those around LDE galaxies by a factor 0.65 +/ 0.12, significant at the 2.9 sigma level. A natural explanation is that the halos of satellite galaxies are stripped through tidal effects in the group environment. Our results are consistent with a typical tidal truncation radius of ~40 kpc.Monthly Notices of the Royal Astronomical Society 01/2013; 431(2). DOI:10.1093/mnras/stt274 · 5.23 Impact Factor 
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ABSTRACT: The Galaxy And Mass Assembly (GAMA) survey is a multiwavelength photometric and spectroscopic survey, using the AAOmega spectrograph on the AngloAustralian Telescope to obtain spectra for up to ~300000 galaxies over 280 square degrees, to a limiting magnitude of r_pet < 19.8 mag. The target galaxies are distributed over 0<z<0.5 with a median redshift of z~0.2, although the redshift distribution includes a small number of systems, primarily quasars, at higher redshifts, up to and beyond z=1. The redshift accuracy ranges from sigma_v~50km/s to sigma_v~100km/s depending on the signaltonoise of the spectrum. Here we describe the GAMA spectroscopic reduction and analysis pipeline. We present the steps involved in taking the raw twodimensional spectroscopic images through to fluxcalibrated onedimensional spectra. The resulting GAMA spectra cover an observed wavelength range of 3750<lambda<8850 A at a resolution of R~1300. The final flux calibration is typically accurate to 1020%, although the reliability is worse at the extreme wavelength ends, and poorer in the blue than the red. We present details of the measurement of emission and absorption features in the GAMA spectra. These measurements are characterised through a variety of quality control analyses detailing the robustness and reliability of the measurements. We illustrate the quality of the measurements with a brief exploration of elementary emission line properties of the galaxies in the GAMA sample. We demonstrate the luminosity dependence of the Balmer decrement, consistent with previously published results, and explore further how Balmer decrement varies with galaxy mass and redshift. We also investigate the mass and redshift dependencies of the [NII]/Halpha vs [OIII]/Hbeta spectral diagnostic diagram, commonly used to discriminate between star forming and nuclear activity in galaxies.Monthly Notices of the Royal Astronomical Society 01/2013; 430(3). DOI:10.1093/mnras/stt030 · 5.23 Impact Factor
Publication Stats
4k  Citations  
480.17  Total Impact Points  
Top Journals
Institutions

2000–2015

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


2014

Scottish Universities Physics Alliance
Glasgow, 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


2006–2009

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


2008

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


2007–2008

Institut d'astrophysique de Paris
Lutetia Parisorum, ÎledeFrance, France


2004–2008

Max Planck Institute for Astronomy
Heidelburg, BadenWürttemberg, Germany


2002–2005

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