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.


Searching for galaxy clusters in the VST-KIDS survey

Astrophysics and Space Science Proceedings 42 (2016) 189-195

M Radovich, E Puddu, F Bellagamba, L Moscardini, M Roncarelli, F Getman, A Grado, V Amaro, A Amon, D Applegate, M Asgari, K Begeman, A Belikov, M Bilicki, C Blake, MB Eriksen, D Boxhoorn, M Brescia, M Brouwer, H Buddelmeijer, A Buddendiek, M Cacciato, Y Cai, M Capaccioli, S Cavuoti, E Chisari, A Choi, OM Cordes, G Covone, M Dal’Ora, JD Jong, A Dvornik, A Edge, T Erben, IF Conti, J Franse, C Georgiou, B Giblin, JH 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, FL 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, BP Pila-Diez, 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. We present the methods and first results of the search for galaxy clusters in the Kilo Degree Survey (KiDS). The adopted algorithm and the criterium for selecting the member galaxies are illustrated. Here we report the preliminary results obtained over a small area (7 deg2), and the comparison of our cluster candidates with those found in the c and SZ Planck catalogues; the analysis to a larger area (148 deg2) is currently in progress. By the KiDS cluster search, we expect to increase the completeness of the clusters catalogue to z = 0.6–0.7 compared to RedMapper.


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.


Early type galaxies and structural parameters from ESO public survey KiDS

Astrophysics and Space Science Proceedings 42 (2016) 135-138

N Roy, NR Napolitano, F La Barbera, C Tortora, F Getman, M Radovich, M Capaccioli, V Amaro, A Amon, D Applegate, M Asgari, K Begeman, A Belikov, M Bilicki, C Blake, MB Eriksen, D Boxhoorn, M Brescia, M Brouwer, H Buddelmeijer, A Buddendiek, M Cacciato, Y Cai, M Capaccioli, S Cavuoti, 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, 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 Kilo Degree survey (KiDS) is a large-scale optical imaging survey carried out with the VLT Survey Telescope (VST), which is the ideal tool for galaxy evolution studies.We expect to observemillions of galaxies for which we extract the structural parameters in four wavebands (u, g, r and i). This sample will represent the largest dataset with measured structural parameters up to a redshift z D 0:5. In this paper we will introduce the sample, and describe the 2D fitting procedure using the 2DPHOT environment and the validation of the parameters with an external catalog.


Euclid space mission: a cosmological challenge for the next 15 years

Proceedings of the International Astronomical Union Cambridge University Press 10 (2015) 375-378

R Scaramella, CS Carvalho, Y Mellier, C Burigana, J Amiaux, J-C Cuillandre, AD Silva, E Maiorano, A Derosa, J Dinis, M Meneghetti, P Franzetti, B Garilli, M Maris, V Cardone, S Wachter, M Cropper, L Amendola, I Tereno, T Kitching, R Massey, H Hoekstra, S Niemi, L Miller, E Semboloni

Euclid is the next ESA mission devoted to cosmology. It aims at observing most of the extragalactic sky, studying both gravitational lensing and clustering over $\sim$15,000 square degrees. The mission is expected to be launched in year 2020 and to last six years. The sheer amount of data of different kinds, the variety of (un)known systematic effects and the complexity of measures require efforts both in sophisticated simulations and techniques of data analysis. We review the mission main characteristics, some aspects of the the survey and highlight some of the areas of interest to this meeting


Intrinsic alignments of galaxies in the Horizon-AGN cosmological hydrodynamical simulation

Monthly Notices of the Royal Astronomical Society Oxford University Press 454 (2015) 2736-2753

N Chisari, C Laigle, S Codis, Y Dubois, C Pichon, J Devriendt, A Slyz, L Miller, R Gavazzi, K Benabed

The intrinsic alignments of galaxies are recognised as a contaminant to weak gravitational lensing measurements. In this work, we study the alignment of galaxy shapes and spins at low redshift ($z\sim 0.5$) in Horizon-AGN, an adaptive-mesh-refinement hydrodynamical cosmological simulation box of 100 Mpc/h a side with AGN feedback implementation. We find that spheroidal galaxies in the simulation show a tendency to be aligned radially towards over-densities in the dark matter density field and other spheroidals. This trend is in agreement with observations, but the amplitude of the signal depends strongly on how shapes are measured and how galaxies are selected in the simulation. Disc galaxies show a tendency to be oriented tangentially around spheroidals in three-dimensions. While this signal seems suppressed in projection, this does not guarantee that disc alignments can be safely ignored in future weak lensing surveys. The shape alignments of luminous galaxies in Horizon-AGN are in agreement with observations and other simulation works, but we find less alignment for lower luminosity populations. We also characterize the systematics of galaxy shapes in the simulation and show that they can be safely neglected when measuring the correlation of the density field and galaxy ellipticities.


Imprint of inflation on galaxy shape correlations

Journal of Cosmology and Astroparticle Physics 2015 (2015)

F Schmidt, NE Chisari, C Dvorkin

We show that intrinsic (not lensing-induced) correlations between galaxy shapes offer a new probe of primordial non-Gaussianity and inflationary physics which is complementary to galaxy number counts. Specifically, intrinsic alignment correlations are sensitive to an anisotropic squeezed limit bispectrum of the primordial perturbations. Such a feature arises in solid inflation, as well as more broadly in the presence of light higher spin fields during inflation (as pointed out recently by Arkani-Hamed and Maldacena). We present a derivation of the all-sky two-point correlations of intrinsic shapes and number counts in the presence of non-Gaussianity with general angular dependence, and show that a quadrupolar (spin-2) anisotropy leads to the analog in galaxy shapes of the well-known scale-dependent bias induced in number counts by isotropic (spin-0) non-Gaussianity. Moreover, in the presence of non-zero anisotropic non-Gaussianity, the quadrupole of galaxy shapes becomes sensitive to far superhorizon modes. These effects come about because long-wavelength modes induce a local anisotropy in the initial power spectrum, with which galaxies will correlate. We forecast that future imaging surveys could provide constraints on the amplitude of anisotropic non-Gaussianity that are comparable to those from the Cosmic Microwave Background (CMB). These are complementary as they probe different physical scales. The constraints, however, depend on the sensitivity of galaxy shapes to the initial conditions which we only roughly estimate from observed tidal alignments.


Revealing a hard X-ray spectral component that reverberates within one light hour of the central supermassive black hole in Ark 564

ASTRONOMY & ASTROPHYSICS 577 (2015) ARTN A8

M Giustini, TJ Turner, JN Reeves, L Miller, E Legg, SB Kraemer, IM George


CFHTLenS: a Gaussian likelihood is a sufficient approximation for a cosmological analysis of third-order cosmic shear statistics

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 449 (2015) 1505-1525

P Simon, E Semboloni, L van Waerbeke, H Hoekstra, T Erben, L Fu, J Harnois-Deraps, C Heymans, H Hildebrandt, M Kilbinger, TD Kitching, L Miller, T Schrabback


CFHTLenS: weak lensing calibrated scaling relations for low-mass clusters of galaxies

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 451 (2015) 1460-1481

K Kettula, S Giodini, E van Uitert, H Hoekstra, A Finoguenov, M Lerchster, T Erben, C Heymans, H Hildebrandt, TD Kitching, A Mahdavi, Y Mellier, L Miller, M Mirkazemi, L Van Waerbeke, J Coupon, E Egami, L Fu, MJ Hudson, JP Kneib, K Kuijken, HJ McCracken, MJ Pereira, B Rowe, T Schrabback, M Tanaka, M Velander


GREAT3 results - I. Systematic errors in shear estimation and the impact of real galaxy morphology

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 450 (2015) 2963-3007

R Mandelbaum, B Rowe, R Armstrong, D Bard, E Bertin, J Bosch, D Boutigny, F Courbin, WA Dawson, A Donnarumma, IF Conti, R Gavazzi, M Gentile, MSS Gill, DW Hogg, EM Huff, MJ Jee, T Kacprzak, M Kilbinger, T Kuntzer, D Lang, W Luo, MC March, PJ Marshall, JE Meyers, L Miller, H Miyatake, R Nakajima, FM Ngole Mboula, G Nurbaeva, Y Okura, S Paulin-Henriksson, J Rhodes, MD Schneider, H Shan, ES Sheldon, M Simet, J-L Starck, F Sureau, M Tewes, KZ Adami, J Zhang, J Zuntz


Cosmological constraints from Subaru weak lensing cluster counts

PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 67 (2015) ARTN 34

T Hamana, J Sakurai, M Koike, L Miller


CFHTLenS: a weak lensing shear analysis of the 3D-Matched-Filter galaxy clusters

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 447 (2015) 1304-1318

J Ford, L Van Waerbeke, M Milkeraitis, C Laigle, H Hildebrandt, T Erben, C Heymans, H Hoekstra, T Kitching, Y Mellier, L Miller, A Choi, J Coupon, L Fu, MJ Hudson, K Kuijken, N Robertson, B Rowe, T Schrabback, M Velander


The galaxy-halo connection from a joint lensing, clustering and abundance analysis in the CFHTLenS/VIPERS field

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 449 (2015) 1352-1379

J Coupon, S Arnouts, L van Waerbeke, T Moutard, O Ilbert, E van Uitert, T Erben, B Garilli, L Guzzo, C Heymans, H Hildebrandt, H Hoekstra, M Kilbinger, T Kitching, Y Mellier, L Miller, M Scodeggio, C Bonnett, E Branchini, I Davidzon, G De Lucia, A Fritz, L Fu, P Hudelot, MJ Hudson, K Kuijken, A Leauthaud, O Le Fevre, HJ McCracken, L Moscardini, BTP Rowe, T Schrabback, E Semboloni, M Velander


First measurement of the cross-correlation of CMB lensing and galaxy lensing

PHYSICAL REVIEW D 91 (2015) ARTN 062001

N Hand, A Leauthaud, S Das, BD Sherwin, GE Addison, JR Bond, E Calabrese, A Charbonnier, MJ Devlin, J Dunkley, T Erben, A Hajian, M Halpern, J Harnois-Deraps, C Heymans, H Hildebrandt, AD Hincks, J-P Kneib, A Kosowsky, M Makler, L Miller, K Moodley, B Moraes, MD Niemack, LA Page, B Partridge, N Sehgal, H Shan, JL Sievers, DN Spergel, ST Staggs, ER Switzer, JE Taylor, L Van Waerbeke, C Welker, EJ Wollack


The masses of satellites in GAMA galaxy groups from 100 square degrees of KiDS weak lensing data

Monthly Notices of the Royal Astronomical Society 454 (2015) 3938-3951

C Sifón, M Cacciato, H Hoekstra, M Brouwer, EV Uitert, M Viola, I Baldry, S Brough, MJI Brown, A Choi, SP Driver, T Erben, A Grado, C Heymans, H Hildebrandt, B Joachimi, JTA de Jong, K Kuijken, J McFarland, L Miller, R Nakajima, N Napolitano, P Norberg, ASG Robotham, P Schneider, GV Kleijn

© 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. We use the first 100 deg2 of overlap between the Kilo-Degree Survey and the Galaxy AndMass Assembly survey to determine the average galaxy halomass 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 group-centric 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 ~ 0.015 Mhost independent of host halo mass, in broad agreement with the expectations of structure formation in a Λ cold dark matter universe.


CFHTLenS: co-evolution of galaxies and their dark matter haloes

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 447 (2015) 298-314

MJ Hudson, BR Gillis, J Coupon, H Hildebrandt, T Erben, C Heymans, H Hoekstra, TD Kitching, Y Mellier, L Miller, L Van Waerbeke, C Bonnett, L Fu, K Kuijken, B Rowe, T Schrabback, E Semboloni, E van Uitert, M Velander


Angular momentum transfer to a Milky Way disc at high redshift

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 449 (2015) 4363-4379

H Tillson, J Devriendt, A Slyz, L Miller, C Pichon


Spectroscopic needs for imaging dark energy experiments

Astroparticle Physics 63 (2015) 81-100

JA Newman, A Abate, FB Abdalla, S Allam, SW Allen, R Ansari, S Bailey, WA Barkhouse, TC Beers, MR Blanton, M Brodwin, JR Brownstein, RJ Brunner, M Carrasco Kind, JL Cervantes-Cota, E Cheu, NE Chisari, M Colless, J Comparat, J Coupon, CE Cunha, A De La Macorra, IP Dell'Antonio, BL Frye, EJ Gawiser, N Gehrels, K Grady, A Hagen, PB Hall, AP Hearin, H Hildebrandt, CM Hirata, S Ho, K Honscheid, D Huterer, Ž Ivezić, JP Kneib, JW Kruk, O Lahav, R Mandelbaum, JL Marshall, DJ Matthews, B Ménard, R Miquel, M Moniez, HW Moos, J Moustakas, AD Myers, C Papovich, JA Peacock, C Park, M Rahman, J Rhodes, JS Ricol, I Sadeh, A Slozar, SJ Schmidt, DK Stern, J Anthony Tyson, A Von Der Linden, RH Wechsler, WM Wood-Vasey, AR Zentner

© 2014 Elsevier B.V. All rights reserved. Ongoing and near-future imaging-based dark energy experiments are critically dependent upon photometric redshifts (a.k.a. photo-z's): i.e., estimates of the redshifts of objects based only on flux information obtained through broad filters. Higher-quality, lower-scatter photo-z's will result in smaller random errors on cosmological parameters; while systematic errors in photometric redshift estimates, if not constrained, may dominate all other uncertainties from these experiments. The desired optimization and calibration is dependent upon spectroscopic measurements for secure redshift information; this is the key application of galaxy spectroscopy for imaging-based dark energy experiments. Hence, to achieve their full potential, imaging-based experiments will require large sets of objects with spectroscopically-determined redshifts, for two purposes: • Training: Objects with known redshift are needed to map out the relationship between object color and z (or, equivalently, to determine empirically-calibrated templates describing the rest-frame spectra of the full range of galaxies, which may be used to predict the color-z relation). The ultimate goal of training is to minimize each moment of the distribution of differences between photometric redshift estimates and the true redshifts of objects, making the relationship between them as tight as possible. The larger and more complete our "training set" of spectroscopic redshifts is, the smaller the RMS photo-z errors should be, increasing the constraining power of imaging experiments. Requirements: Spectroscopic redshift measurements for ∼30,000 objects over > ∼15 widely-separated regions, each at least ∼20 arcmin in diameter, and reaching the faintest objects used in a given experiment, will likely be necessary if photometric redshifts are to be trained and calibrated with conventional techniques. Larger, more complete samples (i.e., with longer exposure times) can improve photo-z algorithms and reduce scatter further, enhancing the science return from planned experiments greatly (increasing the Dark Energy Task Force figure of merit by up to ∼50%). Options: This spectroscopy will most efficiently be done by covering as much of the optical and near-infrared spectrum as possible at modestly high spectral resolution (λ/Δλ > ∼3000), while maximizing the telescope collecting area, field of view on the sky, and multiplexing of simultaneous spectra. The most efficient instrument for this would likely be either the proposed GMACS/MANIFEST spectrograph for the Giant Magellan Telescope or the OPTIMOS spectrograph for the European Extremely Large Telescope, depending on actual properties when built. The PFS spectrograph at Subaru would be next best and available considerably earlier, c. 2018; the proposed ngCFHT and SSST telescopes would have similar capabilities but start later. Other key options, in order of increasing total time required, are the WFOS spectrograph at TMT, MOONS at the VLT, and DESI at the Mayall 4 m telescope (or the similar 4MOST and WEAVE projects); of these, only DESI, MOONS, and PFS are expected to be available before 2020. Table 2-3 of this white paper summarizes the observation time required at each facility for strawman training samples. To attain secure redshift measurements for a high fraction of targeted objects and cover the full redshift span of future experiments, additional near-infrared spectroscopy will also be required; this is best done from space, particularly with WFIRST-2.4 and JWST. Calibration: The first several moments of redshift distributions (the mean, RMS redshift dispersion, etc.), must be known to high accuracy for cosmological constraints not to be systematics-dominated (equivalently, the moments of the distribution of differences between photometric and true redshifts could be determined instead). The ultimate goal of calibration is to characterize these moments for every subsample used in analyses - i.e., to minimize the uncertainty in their mean redshift, RMS dispersion, etc. - rather than to make the moments themselves small. Calibration may be done with the same spectroscopic dataset used for training if that dataset is extremely high in redshift completeness (i.e., no populations of galaxies to be used in analyses are systematically missed). Accurate photo-z calibration is necessary for all imaging experiments. Requirements: If extremely low levels of systematic incompleteness (<∼0.1%) are attained in training samples, the same datasets described above should be sufficient for calibration. However, existing deep spectroscopic surveys have failed to yield secure redshifts for 30-60% of targets, so that would require very large improvements over past experience. This incompleteness would be a limiting factor for training, but catastrophic for calibration. If <∼0.1% incompleteness is not attainable, the best known option for calibration of photometric redshifts is to utilize cross-correlation statistics in some form. The most direct method for this uses cross-correlations between positions on the sky of bright objects of known spectroscopic redshift with the sample of objects that we wish to calibrate the redshift distribution for, measured as a function of spectroscopic z. For such a calibration, redshifts of ∼100,000 objects over at least several hundred square degrees, spanning the full redshift range of the samples used for dark energy, would be necessary.Options: The proposed BAO experiment eBOSS would provide sufficient spectroscopy for basic calibrations, particularly for ongoing and near-future imaging experiments. The planned DESI experiment would provide excellent calibration with redundant cross-checks, but will start after the conclusion of some imaging projects. An extension of DESI to the Southern hemisphere would provide the best possible calibration from cross-correlation methods for DES and LSST. We thus anticipate that our two primary needs for spectroscopy - training and calibration of photometric redshifts - will require two separate solutions. For ongoing and future projects to reach their full potential, new spectroscopic samples of faint objects will be needed for training; those new samples may be suitable for calibration, but the latter possibility is uncertain. In contrast, wide-area samples of bright objects are poorly suited for training, but can provide high-precision calibrations via cross-correlation techniques. Additional training/calibration redshifts and/or host galaxy spectroscopy would enhance the use of supernovae and galaxy clusters for cosmology. We also summarize additional work on photometric redshift techniques that will be needed to prepare for data from ongoing and future dark energy experiments.


Dark matter halo properties of GAMA galaxy groups from 100 square degrees of KiDS weak lensing data

Monthly Notices of the Royal Astronomical Society 452 (2015) 3529-3550

M Viola, M Cacciato, M Brouwer, K Kuijken, H Hoekstra, P Norberg, ASG Robotham, E Van Uitert, M Alpaslan, IK Baldry, A Choi, JTA De Jong, SP Driver, T Erben, A Grado, AW Graham, C Heymans, H Hildebrandt, AM Hopkins, N Irisarri, B Joachimi, J Loveday, L Miller, R Nakajima, P Schneider, C Sifón, G Verdoes Kleijn

© 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. The Kilo-Degree Survey is an optical wide-field survey designed to map the matter distribution in the Universe using weak gravitational lensing. In this paper, we use these data tomeasure 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 (signal-to-noise-ratio ~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-1M⊙. We interpret the results for various subsamples of groups using a halo model framework which accounts for the mis-centring 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 r-band 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 Cosmo-OverWhelmingly Large Simulations project, ruling out models without AGN feedback.

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