We present significant evidence of halo assembly bias for SDSS redMaPPer galaxy clusters in the redshift range $[0.1, 0.33]$. By dividing the 8,648 clusters into two subsamples based on the average member galaxy separation from the cluster center, we
first show that the two subsamples have very similar halo mass of $M_{rm 200m}simeq 1.9times 10^{14}~h^{-1}M_odot$ based on the weak lensing signals at small radii $R<sim 10~h^{-1}{rm Mpc}$. However, their halo bias inferred from both the large-scale weak lensing and the projected auto-correlation functions differs by a factor of $sim$1.5, which is a signature of assembly bias. The same bias hypothesis for the two subsamples is excluded at 2.5$sigma$ in the weak lensing and 4.4$sigma$ in the auto-correlation data, respectively. This result could bring a significant impact on both galaxy evolution and precision cosmology.
The GRavitational lEnsing Accuracy Testing 3 (GREAT3) challenge is an image analysis competition that aims to test algorithms to measure weak gravitational lensing from astronomical images. The challenge started in October 2013 and ends 30 April 2014
. The challenge focuses on testing the impact on weak lensing measurements of realistically complex galaxy morphologies, realistic point spread function, and combination of multiple different exposures. It includes simulated ground- and space-based data. The details of the challenge are described in [15], and the challenge website and its leader board can be found at http://great3challenge.info and http://great3.projects.phys.ucl.ac.uk/leaderboard/, respectively.
A joint analysis of the clustering of galaxies and their weak gravitational lensing signal is well-suited to simultaneously constrain the galaxy-halo connection as well as the cosmological parameters by breaking the degeneracy between galaxy bias and
the amplitude of clustering signal. In a series of two papers, we perform such an analysis at the highest redshift ($zsim0.53$) in the literature using CMASS galaxies in the Sloan Digital Sky Survey-III Baryon Oscillation Spectroscopic Survey Eleventh Data Release (SDSS-III/BOSS DR11) catalog spanning 8300~deg$^2$. In this paper, we present details of the clustering and weak lensing measurements of these galaxies. We define a subsample of 400,916 CMASS galaxies based on their redshifts and stellar mass estimates so that the galaxies constitute an approximately volume-limited and similar population over the redshift range $0.47le zle 0.59$. We obtain a signal-to-noise ratio $S/Nsimeq 56$ for the galaxy clustering measurement. We also explore the redshift and stellar mass dependence of the clustering signal. For the weak lensing measurement, we use existing deeper imaging data from the CFHTLS with publicly available shape and photometric redshift catalogs from CFHTLenS, but only in a 105~deg$^2$ area which overlaps with BOSS. This restricts the lensing measurement to only 5,084 CMASS galaxies. After careful systematic tests, we find a highly significant detection of the CMASS weak lensing signal, with total $S/Nsimeq 26$. These measurements form the basis of the halo occupation distribution and cosmology analysis presented in More et al. (Paper II).
We present a Subaru weak lensing measurement of ACT-CL J0022.2-0036, one of the most luminous, high-redshift (z=0.81) Sunyaev-Zeldovich (SZ) clusters discovered in the 268 deg^2 equatorial region survey of the Atacama Cosmology Telescope. For the wea
k lensing analysis using i-band images, we use a model-fitting (Gauss-Laguerre shapelet) method to measure shapes of galaxy images, where we fit galaxy images in different exposures simultaneously to obtain best-fit ellipticities taking into account the different PSFs in each exposure. We also take into account the astrometric distortion effect on galaxy images by performing the model fitting in the world coordinate system. To select background galaxies behind the cluster at z=0.81, we use photometric redshift (photo-z) estimates for every galaxy derived from the co-added images of multi-passband BrizY, with PSF matching/homogenization. After a photo-z cut for background galaxy selection, we detect the tangential weak lensing distortion signal with a total signal-to-noise ratio of about 3.7. By fitting a Navarro-Frenk-White model to the measured shear profile, we find the cluster mass to be M_200bar{rho}_m = [7.5^+3.2_-2.8(stat.)^+1.3_-0.6(sys.)] x 10^14 M_odot/h. The weak lensing-derived mass is consistent with previous mass estimates based on the SZ observation, with assumptions of hydrostatic equilibrium and virial theorem, as well as with scaling relations between SZ signal and mass derived from weak lensing, X-ray, and velocity dispersion, within the measurement errors. We also show that the existence of ACT-CL J0022.2-0036 at z=0.81 is consistent with the cluster abundance prediction of the Lambda-dominated cold dark matter structure formation model. We thus demonstrate the capability of Subaru-type ground-based images for studying weak lensing of high-redshift clusters.
