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Register a new userA Subaru Weak Lensing Survey I: Cluster Candidates and Spectroscopic Verification
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Authors
Satoshi Miyazaki
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We present the results of an ongoing weak lensing survey conducted with the Subaru telescope whose initial goal is to locate and study the distribution of shear-selected structures or halos. Using a Suprime-cam imaging survey spanning 21.82 square degree, we present a catalog of 100 candidate halos located from lensing convergence maps. Our sample is reliably drawn from that subset of our survey area, (totaling 16.72 square degree) uncontaminated by bright stars and edge effects and limited at a convergence signal to noise ratio of 3.69. To validate the sample detailed spectroscopic measures have been made for 26 candidates using the Subaru multi-object spectrograph, FOCAS. All are confirmed as clusters of galaxies but two arise as the superposition of multiple clusters viewed along the line of sight. Including data available in the literature and an ongoing Keck spectroscopic campaign, a total of 41 halos now have reliable redshifts. For one of our survey fields, the XMM LSS (Pierre et al. 2004) field, we compare our lensing-selected halo catalog with its X-ray equivalent. Of 15 halos detected in the XMM-LSS field, 10 match with published X-ray selected clusters and a further 2 are newly-detected and spectroscopically confirmed in this work. Although three halos have not yet been confirmed, the high success rate within the XMM-LSS field (12/15) confirms that weak lensing provides a reliable method for constructing cluster catalogs, irrespective of the nature of the constituent galaxies or the intracluster medium.
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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 weak 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.
We present results from a weak lensing analysis of the galaxy cluster A1689 (z=0.183) based on deep wide-field imaging data taken with Suprime-Cam on Subaru telescope. A maximum entropy method has been used to reconstruct directly the projected mass distribution of A1689 from combined lensing distortion and magnification measurements of red background galaxies.The resulting mass distribution is clearly concentrated around the cD galaxy, and mass and light in the cluster are similarly distributed in terms of shape and orientation. The azimuthally-averaged mass profile from the two-dimensional reconstruction is in good agreement with the earlier results from the Subaru one-dimensional analysis of the weak lensing data, supporting the assumption of quasi-circular symmetry in the projected mass distribution of the cluster.
We present results from a spectroscopic study of ~4000 galaxies in a 6.2 square degree field in the direction of the Aquarius supercluster and a smaller typical field region in Cetus, down to R<19.5. Galaxy redshifts were measured using the Two Degree Field system on the Anglo-Australian Telescope, and form part of our wider efforts to conduct a spectro-photometric and weak gravitational lensing study of these regions. At the magnitude limit of the survey, we are capable of probing L_* galaxies out to z~0.4. We construct median spectra as a function of various survey parameters as a diagnostic of the quality of the sample. We use the redshift data to identify galaxy clusters and groups within the survey volume. In the Aquarius region, we find a total of 48 clusters and groups, of which 26 are previously unknown systems, and in Cetus we find 14 clusters and groups, of which 12 are new. We estimate centroid redshifts and velocity dispersions for all these systems. In the Aquarius region, we see a superposition of two strong superclusters at z=0.08 and z=0.11, which both have estimated masses and overdensities similar to the Corona Borealis supercluster.
We utilize the galaxy shape catalogue from the first-year data release of the Subaru Hyper Suprime-cam Survey (HSC) to study the dark matter content of galaxy groups in the Universe using weak gravitational lensing. As our lens sample, we use galaxy groups that have been spectroscopically selected from the Galaxy Mass and Assembly galaxy survey in approximately 100 sq. degrees of the sky that overlap with the HSC survey. We restrict our analysis to the 1587 groups with at least five group members. We divide these galaxy groups into six bins each of galaxy group luminosity and group member velocity dispersion and measure the coherent tangential ellipticity pattern on background HSC galaxies imprinted by weak gravitational lensing. We measure the weak lensing signal with a signal-to-noise ratio of 55 and 51 for these two different selections, respectively. We use a Bayesian halo model framework to infer the halo mass distribution of our galaxy groups binned in the two different observable properties and obtain constraints on the power-law scaling relation between mean halo masses and the two group observable properties. We obtain a 5 percent constraint on the amplitude of the scaling relation between halo mass and group luminosity with $langle Mrangle = (0.81pm0.04)times10^{14}h^{-1}M_odot$ for $L_{rm grp}=10^{11.5}h^{-2}L_odot$, and a power-law index of $alpha=1.01pm0.07$. We also obtain a 5-percent constraint on the amplitude of the scaling relation between halo mass and velocity dispersion with $langle Mrangle=(0.93pm0.05)times10^{14}h^{-1}M_odot$ for $sigma=500{,rm kms}^{-1}$ and a power-law index $alpha=1.52pm0.10$, although these scaling relations are sensitive to the exact cuts applied to the number of group members. Comparisons with similar scaling relations from the literature indicate that our results are consistent, but have significantly reduced errors.
Weak gravitational lensing is considered to be one of the most powerful tools to study the mass and the mass distribution of galaxy clusters. However, the mass-sheet degeneracy transformation has limited its success. We present a novel method for a cluster mass reconstruction which combines weak and strong lensing information on common scales and can, as a consequence, break the mass-sheet degeneracy. We extend the weak lensing formalism to the inner parts of the cluster and combine it with the constraints from multiple image systems. We demonstrate the feasibility of the method with simulations, finding an excellent agreement between the input and reconstructed mass also on scales within and beyond the Einstein radius. Using a single multiple image system and photometric redshift information of the background sources used for weak and strong lensing analysis, we find that we are effectively able to break the mass-sheet degeneracy, therefore removing one of the main limitations on cluster mass estimates. We conclude that with high resolution (e.g. HST) imaging data the method can more accurately reconstruct cluster masses and their profiles than currently existing lensing techniques.
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