Publications


Caught in the rhythm: how satellites settle into a plane around their central galaxy

Astronomy and Astrophysics EDP Sciences (2016)

J Devriendt, NE Chisari, C Welker, Y Dubois, C Pichon

Using the cosmological hydrodynamics simulation Horizon-AGN, we investigate the spatial distribution of satellite galaxies relative to their central counterpart in the redshift range between 0.3 and 0.8. We find that, on average, these satellites tend to be located on the galactic plane of the central object. This effect is detected for central galaxies with a stellar mass larger than 10^10 solar masses and found to be strongest for red passive galaxies, while blue galaxies exhibit a weaker trend. For galaxies with a minor axis parallel to the direction of the nearest filament, we find that the coplanarity is stronger in the vicinity of the central galaxy, and decreases when moving towards the outskirts of the host halo. By contrast, the spatial distribution of satellite galaxies relative to their closest filament follows the opposite trend: their tendency to align with them dominates at large distances from the central galaxy, and fades away in its vicinity. Relying on mock catalogs of galaxies in that redshift range, we show that massive red centrals with a spin perpendicular to their filament also have corotating satellites well aligned with both the galactic plane and the filament. On the other hand, lower-mass blue centrals with a spin parallel to their filament have satellites flowing straight along this filament, and hence orthogonally to their galactic plane. The orbit of these satellites is then progressively bent towards a better alignment with the galactic plane as they penetrate the central region of their host halo. The kinematics previously described are consistent with satellite infall and spin build-up via quasi-polar flows, followed by a re-orientation of the spin of massive red galaxies through mergers.


Lensing is low: Cosmology, galaxy formation, or new physics?

Monthly Notices of the Royal Astronomical Society Oxford University Press 467 (2017) 3024-3047

A Leauthaud, S Saito, S Hilbert, A Barreira, S More, M White, S Alam, P Behroozi, K Bundy, J Coupon, T Erben, C Heymans, H Hildebrandt, R Mandelbaum, L Miller, MES Pereira, B Moraes, SA Rodriguez-Torres, F Schmidt, H-Y Shan, F Villaescusa-Navarro, M Viel

We present high signal-to-noise galaxy-galaxy lensing measurements of the BOSS CMASS sample using 250 square degrees of weak lensing data from CFHTLenS and CS82. We compare this signal with predictions from mock catalogs trained to match observables including the stellar mass function and the projected and two dimensional clustering of CMASS. We show that the clustering of CMASS, together with standard models of the galaxy-halo connection, robustly predicts a lensing signal that is 20-40% larger than observed. Detailed tests show that our results are robust to a variety of systematic effects. Lowering the value of $S_{\rm 8}=\sigma_{\rm 8} \sqrt{\Omega_{\rm m}/0.3}$ compared to Planck2015 reconciles the lensing with clustering. However, given the scale of our measurement ($r<10$ $h^{-1}$ Mpc), other effects may also be at play and need to be taken into consideration. We explore the impact of baryon physics, assembly bias, massive neutrinos, and modifications to general relativity on $\Delta\Sigma$ and show that several of these effects may be non-negligible given the precision of our measurement. Disentangling cosmological effects from the details of the galaxy-halo connection, the effects of baryons, and massive neutrinos, is the next challenge facing joint lensing and clustering analyses. This is especially true in the context of large galaxy samples from Baryon Acoustic Oscillation surveys with precise measurements but complex selection functions.


Cross-correlating Planck tSZ with RCSLenS weak lensing: Implications for cosmology and AGN feedback

Monthly Notices of the Royal Astronomical Society Oxford University Press 460 (2016) 434-457

A Hojjati, T Tröster, J Harnois-Déraps, IG McCarthy, L van Waerbeke, A Choi, T Erben, C Heymans, H Hildebrandt, G Hinshaw, Y-Z Ma, L Miller, M Viola, H Tanimura

We present measurements of the spatial mapping between (hot) baryons and the total matter in the Universe, via the cross-correlation between the thermal Sunyaev-Zeldovich (tSZ) map from Planck and the weak gravitational lensing maps from the Red Sequence Cluster Survey (RCSLenS). The cross-correlations are performed on the map level where all the sources (including diffuse intergalactic gas) contribute to the signal. We consider two configuration-space correlation function estimators, $\xi^{ y-\kappa}$ and $\xi^ {y-\gamma_{t}}$, and a Fourier space estimator, $C_{\ell}^{y-\kappa}$, in our analysis. We detect a significant correlation out to three degrees of angular separation on the sky. Based on statistical noise only, we can report 13$\sigma$ and 17$\sigma$ detections of the cross-correlation using the configuration-space $y-\kappa$ and $y-\gamma_{t}$ estimators, respectively. Including a heuristic estimate of the sampling variance yields a detection significance of 6$\sigma$ and 8$\sigma$, respectively. A similar level of detection is obtained from the Fourier-space estimator, $C_{\ell}^{y-\kappa}$. As each estimator probes different dynamical ranges, their combination improves the significance of the detection. We compare our measurements with predictions from the cosmo-OWLS suite of cosmological hydrodynamical simulations, where different galactic feedback models are implemented. We find that a model with considerable AGN feedback that removes large quantities of hot gas from galaxy groups and WMAP-7yr best-fit cosmological parameters provides the best match to the measurements. All baryonic models in the context of a Planck cosmology over-predict the observed signal. Similar cosmological conclusions are drawn when we employ a halo model with the observed `universal' pressure profile.


KiDS-450: Testing extensions to the standard cosmological model

Monthly Notices of the Royal Astronomical Society Oxford University Press (2017)

S Joudaki, A Mead, C Blake, A Choi, H Hildebrandt, H Hoekstra, D Klaes, F Köhlinger, L Miller, P Schneider, J de Jong, T Erben, C Heymans, B Joachimi, J McFarland, K Kuijken, M Viola

We test extensions to the standard cosmological model with weak gravitational lensing tomography using 450 deg$^2$ of imaging data from the Kilo Degree Survey (KiDS). In these extended cosmologies, which include massive neutrinos, nonzero curvature, evolving dark energy, modified gravity, and running of the scalar spectral index, we also examine the discordance between KiDS and cosmic microwave background measurements from Planck. The discordance between the two datasets is largely unaffected by a more conservative treatment of the lensing systematics and the removal of angular scales most sensitive to nonlinear physics. The only extended cosmology that simultaneously alleviates the discordance with Planck and is at least moderately favored by the data includes evolving dark energy with a time-dependent equation of state (in the form of the $w_0-w_a$ parameterization). In this model, the respective $S_8 = \sigma_8 \sqrt{\Omega_{\rm m}/0.3}$ constraints agree at the $1\sigma$ level, and there is `substantial concordance' between the KiDS and Planck datasets when accounting for the full parameter space. Moreover, the Planck constraint on the Hubble constant is wider than in LCDM and in agreement with the Riess et al. (2016) direct measurement of $H_0$. The dark energy model is moderately favored as compared to LCDM when combining the KiDS and Planck measurements, and remains moderately favored after including an informative prior on the Hubble constant. In both of these scenarios, the dark energy parameters are discrepant with a cosmological constant at the $3\sigma$ level. Moreover, KiDS constrains the sum of neutrino masses to 4.0 eV (95% CL), finds no preference for time or scale dependent modifications to the metric potentials, and is consistent with flatness and no running of the spectral index. The analysis code is publicly available at https://github.com/sjoudaki/kids450


Calibration of weak-lensing shear in the Kilo-Degree Survey

Monthly Notices of the Royal Astronomical Society Oxford University Press 467 (2017) 1627-1651

I Fenech Conti, RTL Herbonnet, H Hoekstra, J Merten, L Miller, M Viola

We describe and test the pipeline used to measure the weak lensing shear signal from the Kilo Degree Survey (KiDS). It includes a novel method of `self-calibration' that partially corrects for the effect of noise bias. We also discuss the `weight bias' that may arise in optimally-weighted measurements, and present a scheme to mitigate that bias. To study the residual biases arising from both galaxy selection and shear measurement, and to derive an empirical correction to reduce the shear biases to $\lesssim 1\%$, we create a suite of simulated images whose properties are close to those of the KiDS survey observations. We find that the use of `self-calibration' reduces the additive and multiplicative shear biases significantly, although further correction via a calibration scheme is required, which also corrects for a dependence of the bias on galaxy properties. We find that the calibration relation itself is biased by the use of noisy, measured galaxy properties, which may limit the final accuracy that can be achieved. We assess the accuracy of the calibration in the tomographic bins used for the KiDS cosmic shear analysis, testing in particular the effect of possible variations in the uncertain distributions of galaxy size, magnitude and ellipticity, and conclude that the calibration procedure is accurate at the level of multiplicative bias $\lesssim 1\%$ required for the KiDS cosmic shear analysis.


KiDS-450: Cosmological parameter constraints from tomographic weak gravitational lensing

Monthly Notices of the Royal Astronomical Society 465 (2016) 1-50

H Hildebrandt, M Viola, C Heymans, S Joudaki, K Kuijken, C Blake, T Erben, B Joachimi, D Klaes, L Miller, CB Morrison, R Nakajima, G Verdoes Kleijn, A Amon, A Choi, G Covone, JTA de Jong, A Dvornik, I Fenech Conti, A Grado, J Harnois-Déraps, R Herbonnet, H Hoekstra, F Köhlinger, J McFarland, A Mead, J Merten, N Napolitano, JA Peacock, M Radovich, P Schneider, P Simon, EA Valentijn, JL van den Busch, E van Uitert, L Van Waerbeke

We present cosmological parameter constraints from a tomographic weak gravitational lensing analysis of ~450 deg 2 of imaging data from the Kilo Degree Survey (KiDS). For a flat λCDM cosmology with a prior on H 0 that encompasses the most recent direct measurements, we find S 8 ≡ σ 8 √ω m /0.3 = 0.745±0.039. This result is in good agreement with other low redshift probes of large scale structure, including recent cosmic shear results, along with pre-Planck cosmic microwave background constraints. A 2.3-σ tension in S 8 and `substantial discordance' in the full parameter space is found with respect to the Planck 2015 results. We use shear measurements for nearly 15 million galaxies, determined with a new improved `self-calibrating' version of lens fit validated using an extensive suite of image simulations. Four-band ugri photometric redshifts are calibrated directly with deep spectroscopic surveys. The redshift calibration is confirmed using two independent tech- niques based on angular cross-correlations and the properties of the photometric redshift probability distributions. Our covariance matrix is determined using an analytical approach, verified numeri- cally with large mock galaxy catalogues. We account for uncertainties in the modelling of intrinsic galaxy alignments and the impact of baryon feedback on the shape of the non-linear matter power spectrum, in addition to the small residual uncertainties in the shear and redshift calibration. The cosmology analysis was performed blind. Our high-level data products, including shear correlation functions, covariance matrices, redshift distributions, and Monte Carlo Markov Chains.


CODEX weak lensing: Concentration of galaxy clusters at z ~ 0.5

Monthly Notices of the Royal Astronomical Society Oxford University Press 468 (2017) 1092-1116

N Cibirka, ES Cypriano, F Brimioulle, D Gruen, T Erben, L Miller, L van Waerbeke, A Finoguenov, C Kirkpatrick, JP Henry, E Rykoff, E Rozo, RA Dupke, J-P Kneib, H Shan, P Spinelli

We present a stacked weak lensing analysis of 27 richness selected galaxy clusters at $0.40 \leqslant z \leqslant 0.62$ in the CODEX survey. The fields were observed in 5 bands with the CFHT. We measure the stacked surface mass density profile with a $14\sigma$ significance in the radial range $0.1 < R\ Mpc\ h^{-1} < 2.5$. The profile is well described by the halo model, with the main halo term following an NFW profile and including the off-centring effect. We select the background sample using a conservative colour-magnitude method to reduce the potential systematic errors and contamination by cluster member galaxies. We perform a Bayesian analysis for the stacked profile and constrain the best-fit NFW parameters $M_{200c} = 6.6^{+1.0}_{-0.8} \times 10^{14} h^{-1} M_{\odot}$ and $c_{200c} = 3.7^{+0.7}_{-0.6}$. The off-centring effect was modelled based on previous observational results found for redMaPPer SDSS clusters. Our constraints on $M_{200c}$ and $c_{200c}$ allow us to investigate the consistency with numerical predictions and select a concentration-mass relation to describe the high richness CODEX sample. Comparing our best-fit values for $M_{200c}$ and $c_{200c}$ with other observational surveys at different redshifts, we find no evidence for evolution in the concentration-mass relation, though it could be mitigated by particular selection functions. Similar to previous studies investigating the X-ray luminosity-mass relation, our data suggests a lower evolution than expected from self-similarity.


The Horizon-AGN simulation: evolution of galaxy properties over cosmic time

arXiv (2016)

E Chisari, S Peirani, S Kaviraj, A Slyz, C Laigle, J Devriendt, T Kimm, Y Dubois, C Pichon

We compare the predictions of Horizon-AGN, a hydro-dynamical cosmological simulation that uses an adaptive mesh refinement code, to observational data in the redshift range 0 < z > 6. We study the reproduction, by the simulation, of quantities that trace the aggregate stellar-mass growth of galaxies over cosmic time: luminosity and stellar-mass functions, the star formation main sequence, rest-frame UV-optical-near infrared colours and the cosmic star-formation history. We show that Horizon-AGN, which is not tuned to reproduce the local Universe, produces good overall agreement with these quantities, from the present day to the epoch when the Universe was 5% of its current age. By comparison to Horizon-noAGN, a twin simulation without AGN feedback, we quantify how feedback from black holes is likely to help shape galaxy stellar-mass growth in the redshift range 0 < z > 6, particularly in the most massive galaxies. Our results demonstrate that Horizon-AGN successfully captures the evolutionary trends of observed galaxies over the lifetime of the Universe, making it an excellent tool for studying the processes that drive galaxy evolution and making predictions for the next generation of galaxy surveys.


KiDS-450: The tomographic weak lensing power spectrum and constraints on cosmological parameters

Monthly Notices of the Royal Astronomical Society Oxford University Press 471 (2017) 4412–4435-

A Choi, D Klaes, L Miller, F Köhlinger, M Viola, B Joachimi, H Hoekstra, EV Uitert, H Hildebrandt, T Erben, C Heymans, S Joudaki, K Kuijken, J Merten, P Schneider, EA Valentijn

We present measurements of the weak gravitational lensing shear power spectrum based on $450$ sq. deg. of imaging data from the Kilo Degree Survey. We employ a quadratic estimator in two and three redshift bins and extract band powers of redshift auto-correlation and cross-correlation spectra in the multipole range $76 \leq \ell \leq 1310$. The cosmological interpretation of the measured shear power spectra is performed in a Bayesian framework assuming a $\Lambda$CDM model with spatially flat geometry, while accounting for small residual uncertainties in the shear calibration and redshift distributions as well as marginalising over intrinsic alignments, baryon feedback and an excess-noise power model. Moreover, massive neutrinos are included in the modelling. The cosmological main result is expressed in terms of the parameter combination $S_8 \equiv \sigma_8 \sqrt{\Omega_{\rm m}/0.3}$ yielding $S_8 = \ 0.651 \pm 0.058$ (3 z-bins), confirming the recently reported tension in this parameter with constraints from Planck at $3.2\sigma$ (3 z-bins). We cross-check the results of the 3 z-bin analysis with the weaker constraints from the 2 z-bin analysis and find them to be consistent. The high-level data products of this analysis, such as the band power measurements, covariance matrices, redshift distributions, and likelihood evaluation chains are available at http://kids.strw.leidenuniv.nl/


Measuring light echoes in NGC 4051

Monthly Notices of the Royal Astronomical Society Oxford University Press 467 (2017) 3924-3933

TJ Turner, L Miller, JN Reeves, V Braito

Five archived X-ray observations of NGC 4051, taken using the NuSTAR observatory, have been analysed, revealing lags between flux variations in bands covering a wide range of X-ray photon energy. In all pairs of bands compared, the harder band consistently lags the softer band by at least 1000s, at temporal frequencies ~5E-5 Hz. In addition, soft-band lags up to 400s are measured at frequencies ~2E-4 Hz. Light echos from an excess of soft band emission in the inner accretion disk cannot explain the lags in these data, as they are seen in cross-correlations with energy bands where the softer band is expected to have no contribution from reflection. The basic properties of the time delays have been parameterised by fitting a top hat response function that varies with photon energy, taking fully into account the covariance between measured time lag values. The low-frequency hard-band lags and the transition to soft-band lags are consistent with time lags arising as reverberation delays from circumnuclear scattering of X-rays, although greater model complexity is required to explain the entire spectrum of lags. The scattered fraction increases with increasing photon energy as expected, and the scattered fraction is high, indicating the reprocessor to have a global covering fraction ~50% around the continuum source. Circumnuclear material, possibly associated with a disk wind at a few hundred gravitational radii from the primary X-ray source, may provide suitable reprocessing.


Galaxy-halo alignments in the Horizon-AGN cosmological hydrodynamical simulation

Monthly Notices of the Royal Astronomical Society Oxford University Press (2017)

NE Chisari, N Koukoufilippas, A Jindal, JEG Devriendt, S Peirani, RS Beckmann, S Codis, L Miller, Y Dubois, CMC Laigle, A Slyz, C Pichon

Intrinsic alignments of galaxies are a significant astrophysical systematic affecting cosmological constraints from weak gravitational lensing. Obtaining numerical predictions from hydrodynamical simulations of expected survey volumes is expensive, and a cheaper alternative relies on populating large dark matter-only simulations with accurate models of alignments calibrated on smaller hydrodynamical runs. This requires connecting the shapes and orientations of galaxies to those of dark matter halos and to the large-scale structure. In this paper, we characterise galaxy-halo alignments in the Horizon-AGN cosmological hydrodynamical simulation. We compare the shapes and orientations of galaxies in the redshift range $0


CFHTLenS and RCSLenS cross-correlation with Planck lensing detected in fourier and configuration space

Monthly Notices of the Royal Astronomical Society 460 (2016) 434-457

J Harnois-Déraps, T Tröster, A Hojjati, L van Waerbeke, M Asgari, A Choi, T Erben, C Heymans, H Hildebrandt, TD Kitching, L Miller, R Nakajima, M Viola, S Arnouts, J Coupon, T Moutard


Multitracing anisotropic non-Gaussianity with galaxy shapes

Physical Review D American Physical Society 94 (2016) 123507

N Chisari, C Dvorkin, F Schmidt, DN Spergel

Correlations between intrinsic galaxy shapes on large scales arise due to the effect of the tidal field of the large-scale structure. Anisotropic primordial non-Gaussianity induces a distinct scale-dependent imprint in these tidal alignments on large scales. Motivated by the observational finding that the alignment strength of luminous red galaxies depends on how galaxy shapes are measured, we study the use of two different shape estimators as a multitracer probe of intrinsic alignments. We show, by means of a Fisher analysis, that this technique promises a significant improvement on anisotropic non-Gaussianity constraints over a singletracer method. For future weak lensing surveys, the uncertainty in the anisotropic non-Gaussianity parameter, A 2 , is forecast to be σ(A 2 ) ≈ 50, ∼40% smaller than currently available constraints from the bispectrum of the cosmic microwave background. This corresponds to an improvement of a factor of 4-5 over the uncertainty from a single-tracer analysis.


Galaxy evolutionwithin the kilo-degree survey

Astrophysics and Space Science Proceedings 42 (2016) 123-128

C Tortora, NR Napolitano, F La Barbera, N Roy, M Radovich, F Getman, M Brescia, S Cavuoti, M Capaccioli, G Longo, V Amaro, A Amon, D Applegate, M Asgari, K Begeman, A Belikov, M Bilicki, C Blake, MB Eriksen, D Boxhoorn, M Brouwer, H Buddelmeijer, A Buddendiek, M Cacciato, Y Cai, M Capaccioli, E Chisari, A Choi, OM Cordes, G Covone, M Dall’Ora, J de Jong, A Dvornik, A Edge, T Erben, IF Conti, J Franse, C Georgiou, F Getman, B Giblin, A Grado, J Harnois-Déraps, E Helmich, R Herbonnet, C Heymans, H Hildebrandt, H Hoekstra, A Hojjati, Z Huang, N Irisarri, A Jakobs, B Joachimi, A Johnson, H Johnston, S Joudaki, F Köhlinger, T Kitching, D Klaes, L Koopmans, K Kuijken, F La Barbera, P Lacerda, G Longo, J McFarland, A Mead, J Merten, L Miller, C Morrison, R Nakajima, N Napolitano, M Paolillo, J Peacock, R Peletier, CE Petrillo, B Pila-Diez, E Puddu, M Radovich, A Rifatto, N Roy, P Schneider, T Schrabback, E Semboloni, C Sifon, G Sikkema, P Simon, W Sutherland, C Tortora, T Troester, A Tudorica, E Valentijn, R Van Der Burg, E Van Uitert, L Van Waerbeke, GV Kleijn, M Viola, WJ Vriend, KZ Adami

© Springer International Publishing Switzerland 2016. The ESO Public Kilo-Degree Survey (KiDS) is an optical wide-field imaging survey carried out with the VLT Survey Telescope and the OmegaCAM camera. KiDS will scan 1,500 deg2in four optical filters (u, g, r, i). Designed to be a weak lensing survey, it is ideal for galaxy evolution studies, thanks to the high spatial resolution of VST, the excellent seeing and the photometric depth. The surface photometry has provided with structural parameters (e.g. size and Sérsic index), aperture and total magnitudes have been used to obtain photometric redshifts from Machine Learning methods and stellar masses/luminositites from stellar population synthesis. Our project aimed at investigating the evolution of the colour and structural properties of galaxies with mass and environment up to redshift z ~ 0:5 and more, to put constraints on galaxy evolution processes, as galaxy mergers.


The stellar-to-halo mass relation of GAMA galaxies from 100 deg 2 of KiDS weak lensing data

Monthly Notices of the Royal Astronomical Society Oxford University Press 459 (2016) 3251-3270

I Baldry, J Bland-Hawthorn, SP Driver, T Erben, H Hildebrandt, B Joachimi, J Liske, J Loveday, R Nakajima, J Peacock, M Radovich, ASG Robotham, P Schneider, E van Uitert, M Cacciato, H Hoekstra, M Brouwer, C Sifón, M Viola, S Brough, MJI Brown, A Choi, C Heymans, K Kuijken, J McFarland

We study the stellar-to-halo mass relation of central galaxies in the range 9.7 < log10(M*/h-2 M⊙) < 11.7 and z < 0.4, obtained from a combined analysis of the Kilo Degree Survey (KiDS) and the Galaxy And Mass Assembly (GAMA) survey. We use ~100 deg2 of KiDS data to study the lensing signal around galaxies for which spectroscopic redshifts and stellar masses were determined by GAMA. We show that lensing alone results in poor constraints on the stellar-to-halo mass relation due to a degeneracy between the satellite fraction and the halo mass, which is lifted when we simultaneously fit the stellar mass function. At M* > 5 × 1010 h-2 M⊙, the stellar mass increases with halo mass as ~Mh0.25. The ratio of dark matter to stellar mass has a minimum at a halo mass of 8 × 1011 h-1 M⊙ with a value of Mh/M* = 56-10+16 [h]. We also use the GAMA group catalogue to select centrals and satellites in groups with five or more members, which trace regions in space where the local matter density is higher than average, and determine for the first time the stellar-to-halo mass relation in these denser environments. We find no significant differences compared to the relation from the full sample, which suggests that the stellar-to-halo mass relation does not vary strongly with local density. Furthermore, we find that the stellar-to-halo mass relation of central galaxies can also be obtained by modelling the lensing signal and stellar mass function of satellite galaxies only, which shows that the assumptions to model the satellite contribution in the halo model do not significantly bias the stellar-to-halo mass relation. Finally, we show that the combination of weak lensing with the stellar mass function can be used to test the purity of group catalogues.


Radio weak lensing shear measurement in the visibility domain – I. Methodology

Monthly Notices of the Royal Astronomical Society Oxford University Press 463 (2016) 1881-1890

M Rivi, L Miller, S Makhathini, FB Abdalla

The high sensitivity of the new generation of radio telescopes such as the Square Kilometre Array (SKA) will allow cosmological weak lensing measurements at radio wavelengths that are competitive with optical surveys. We present an adaptation to radio data of lensfit, a method for galaxy shape measurement originally developed and used for optical weak lensing surveys. This likelihood method uses an analytical galaxy model and makes a Bayesian marginalization of the likelihood over uninteresting parameters. It has the feature of working directly in the visibility domain, which is the natural approach to adopt with radio interferometer data, avoiding systematics introduced by the imaging process. As a proof of concept, we provide results for visibility simulations of individual galaxies with flux density S ≥ 10 μJy at the phase centre of the proposed SKA1-MID baseline configuration, adopting 12 frequency channels in the band 950–1190 MHz. Weak lensing shear measurements from a population of galaxies with realistic flux and scalelength distributions are obtained after natural gridding of the raw visibilities. Shear measurements are expected to be affected by ‘noise bias’: we estimate the bias in the method as a function of signal-to-noise ratio (SNR). We obtain additive and multiplicative bias values that are comparable to SKA1 requirements for SNR > 18 and SNR > 30, respectively. The multiplicative bias for SNR >10 is comparable to that found in ground-based optical surveys such as CFHTLenS, and we anticipate that similar shear measurement calibration strategies to those used for optical surveys may be used to good effect in the analysis of SKA radio interferometer data.


RCSLenS: the Red Cluster Sequence Lensing Survey

Monthly Notices of the Royal Astronomical Society Oxford University Press 463 (2016) 635-654

H Hildebrandt, A Choi, C Heymans, C Blake, T Erben, L Miller, R Nakajima, L van Waerbeke, M Viola, A Buddendiek, J Harnois-Déraps, B Joachimi, A Hojjati, TD Kitching, S Joudaki, S Gwyn, C Wolf, N Johnson, K Kuijken, Z Sheikhbahaee, A Tudorica, HKC Yee

We present the Red-sequence Cluster Lensing Survey (RCSLenS), an application of the methods developed for the Canada France Hawaii Telescope Lensing Survey (CFHTLenS) to the ~785deg$^2$, multi-band imaging data of the Red-sequence Cluster Survey 2 (RCS2). This project represents the largest public, sub-arcsecond seeing, multi-band survey to date that is suited for weak gravitational lensing measurements. With a careful assessment of systematic errors in shape measurements and photometric redshifts we extend the use of this data set to allow cross-correlation analyses between weak lensing observables and other data sets. We describe the imaging data, the data reduction, masking, multi-colour photometry, photometric redshifts, shape measurements, tests for systematic errors, and a blinding scheme to allow for more objective measurements. In total we analyse 761 pointings with r-band coverage, which constitutes our lensing sample. Residual large-scale B-mode systematics prevent the use of this shear catalogue for cosmic shear science. The effective number density of lensing sources over an unmasked area of 571.7deg$^2$ and down to a magnitude limit of r~24.5 is 8.1 galaxies per arcmin$^2$ (weighted: 5.5 arcmin$^{-2}$) distributed over 14 patches on the sky. Photometric redshifts based on 4-band griz data are available for 513 pointings covering an unmasked area of 383.5 deg$^2$ We present weak lensing mass reconstructions of some example clusters as well as the full survey representing the largest areas that have been mapped in this way. All our data products are publicly available through CADC at http://www.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/en/community/rcslens/query.html in a format very similar to the CFHTLenS data release.


THE GLOBAL IMPLICATIONS OF THE HARD EXCESS. II. ANALYSIS OF THE LOCAL POPULATION OF RADIO-QUIET AGNs

ASTROPHYSICAL JOURNAL 818 (2016) ARTN 12

MM Tatum, TJ Turner, L Miller, JN Reeves, J DiLiello, J Gofford, A Patrick, M Clayton


The SuperCOSMOS all-sky galaxy catalogue

Monthly Notices of the Royal Astronomical Society Oxford University Press 462 (2016) 2085-2098

JA Peacock, NC Hambly, M Bilicki, HT MacGillivray, L Miller, MA Read, SB Tritton

We describe the construction of an all-sky galaxy catalogue, using SuperCOSMOS scans of Schmidt photographic plates from theUKSchmidt Telescope and Second Palomar Observatory Sky Survey. The photographic photometry is calibrated using Sloan Digital Sky Survey data, with results that are linear to 2 per cent or better. All-sky photometric uniformity is achieved by matching plate overlaps and also by requiring homogeneity in optical-to-2MASS colours, yielding zero-points that are uniform to 0.03 mag or better. The typical AB depths achieved are BJ < 21, RF < 19.5 and IN < 18.5, with little difference between hemispheres. In practice, the IN plates are shallower than the BJ and RF plates, so for most purposes we advocate the use of a catalogue selected in these two latter bands. At high Galactic latitudes, this catalogue is approximately 90 per cent complete with 5 per cent stellar contamination; we quantify how the quality degrades towards the Galactic plane. At low latitudes, there are many spurious galaxy candidates resulting from stellar blends: these approximately match the surface density of true galaxies at |b| = 30°. Above this latitude, the catalogue limited in BJ and RF contains in total about 20 million galaxy candidates, of which 75 per cent are real. This contamination can be removed, and the sky coverage extended, by matching with additional data sets. This SuperCOSMOS catalogue has been matched with 2MASS and with WISE, yielding quasiall- sky samples of respectively 1.5 million and 18.5 million galaxies, to median redshifts of 0.08 and 0.20. This legacy data set thus continues to offer a valuable resource for large-angle cosmological investigations.


Weak-lensing mass calibration of the Atacama Cosmology Telescope equatorial Sunyaev-Zeldovich cluster sample with the Canada-France-Hawaii telescope stripe 82 survey

Journal of Cosmology and Astroparticle Physics IOP Publishing 2016 (2016) 013-

N Battaglia, A Leauthaud, H Miyatake, M Hasselfield, MB Gralla, R Allison, JR Bond, E Calabrese, D Crichton, MJ Devlin, R Dünner, J Dunkley, T Erben, S Ferrara, M Halpern, M Hilton, JC Hill, AD Hincks, R Hložek, KM Huffenberger, JP Hughes, JP Kneib, A Kosowsky, M Makler, TA Marriage

Mass calibration uncertainty is the largest systematic effect for using clusters of galaxies to constrain cosmological parameters. We present weak lensing mass measurements from the Canada-France-Hawaii Telescope Stripe 82 Survey for galaxy clusters selected through their high signal-to-noise thermal Sunyaev-Zeldovich (tSZ) signal measured with the Atacama Cosmology Telescope (ACT). For a sample of 9 ACT clusters with a tSZ signal-to-noise greater than five the average weak lensing mass is (4.8±0.8) ×1014 Mo, consistent with the tSZ mass estimate of (4.70±1.0) ×1014 Mo which assumes a universal pressure profile for the cluster gas. Our results are consistent with previous weak-lensing measurements of tSZ-detected clusters from the Planck satellite. When comparing our results, we estimate the Eddington bias correction for the sample intersection of Planck and weak-lensing clusters which was previously excluded.

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