Gravitational Lensing by NFW Halos

156

179

We present weak-lensing mass measurements of 50 X-ray luminous galaxy clusters at 0.15 z 0.3, based on uniform high quality observations with Suprime-Cam mounted on the 8.2-m Subaru telescope. We pay close attention to possible systematic biases, aiming to control them at the ∼ < 4 per cent level. The dominant source of systematic bias in weak-lensing measurements of the mass of individual galaxy clusters is contamination of background galaxy catalogues by faint cluster and foreground galaxies. We extend our conservative method for selecting background galaxies with (V − i ′ ) colours redder than the red sequence of cluster members to use a colour-cut that depends on cluster-centric radius. This allows us to define background galaxy samples that suffer 1 per cent contamination, and comprise 13 galaxies per square arcminute. Thanks to the purity of our background galaxy catalogue, the largest systematic that we identify in our analysis is a shape measurement bias of 3 per cent, that we measure using simulations that probe weak shears upto g = 0.3. Our individual cluster mass and concentration measurements are in excellent agreement with predictions of the mass-concentration relation. Equally, our stacked shear profile is in excellent agreement with the Navarro Frenk and White profile. Our new LoCuSS mass measurements are consistent with the CCCP and CLASH surveys, and in tension with the Weighing the Giants at ∼ 1 − 2σ significance. Overall, the consensus at z 0.3 that is emerging from these complementary surveys represents important progress for cluster mass calibration, and augurs well for cluster cosmology.

Section: Mass Measurementsmentioning

confidence: 99%

LoCuSS: weak-lensing mass calibration of galaxy clusters

Okabe

Smith

2016

156

179

“…The expression used to fit the weak lensing shear profiles (under the assumption of an underlying NFW profile) for comparison is given in Wright & Brainerd 2000. To recap, our method makes the following assumptions: that modifications to general relativity include a chameleon screening mechanism and can be described by Equation 1; that dark matter halos follow an NFW profile (Equation 4); that a fifth force can be included in the hydrostatic equilibrium expression according to Equation 9; that clusters of galaxies are isolated, isothermal, and spherical (which in turn implies that the clusters are in hydrostatic equilibrium, have an electron number density that follows a beta-model, and their X-ray emission can be predicted from a thermal cooling function); and that the weak lensing shear profiles of clusters are given in Wright & Brainerd 2000. We discuss the impact of some of these assumptions in Section 5.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

TheXMMCluster Survey: testing chameleon gravity using the profiles of clusters

Wilcox¹,

Bacon²,

Nichol³

et al. 2015

108

116

The chameleon gravity model postulates the existence of a scalar field that couples with matter to mediate a fifth force. If it exists, this fifth force would influence the hot X-ray emitting gas filling the potential wells of galaxy clusters. However, it would not influence the clusters weak lensing signal. Therefore, by comparing X-ray and weak lensing profiles, one can place upper limits on the strength of a fifth force. This technique has been attempted before using a single, nearby cluster (Coma, z = 0.02, Terukina et al. 2014). Here we apply the technique to the stacked profiles of 58 clusters at higher redshifts (0.1 < z < 1.2 ), including 12 new to the literature, using X-ray data from the XMM Cluster Survey (XCS) and weak lensing data from the Canada France Hawaii Telescope Lensing Survey (CFHTLenS). Using a multiparameter MCMC analysis, we constrain the two chameleon gravity parameters (β and φ ∞ ). Our fits are consistent with general relativity, not requiring a fifth force. In the special case of f (R) gravity (where β = 1/6), we set an upper limit on the background field amplitude today of |f R0 |< 6 × 10 −5 (95% CL). This is one of the strongest constraints to date on |f R0 | on cosmological scales. We hope to improve this constraint in future by extending the study to hundreds of clusters using data from the Dark Energy Survey.

“…We use the analytical expression for the projected surface density of an NFW profile, NFW (R), derived by Wright & Brainerd (2000). In reality, we observe a sample of satellites at different distances to their respective group centres; therefore the total group contribution is…”

Section: Host Group Contributionmentioning

confidence: 99%

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

Sifón¹,

Cacciato²,

Hoekstra³

et al. 2015

We use the first 100 deg 2 of overlap between the Kilo-Degree Survey (KiDS) and the Galaxy And Mass Assembly (GAMA) survey to determine the galaxy halo mass of ∼10,000 spectroscopically-confirmed satellite galaxies in massive (M > 10 13 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 (NFW) density profiles, fully accounting for the data covariance. The probed satellite galaxies in these groups have total masses log M sub /(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 /M sub ≈ 0.04 h −1 . The average subhalo hosting these satellite galaxies has a mass M sub ∼ 0.015M host independent of host halo mass, in broad agreement with the expectations of structure formation in a ΛCDM universe.