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The CLASH Survey (Cluster Lensing And Supernova survey with Hubble)
Left: HST image of the central region of MACS J1206.2-0847, an X-ray-selected CLASH cluster at a redshift of 0.44. See the press release by the CLASH team.
Lower left: Mass distribution (white contours) in and around the CLASH cluster MACSJ1206.2-0847 reconstructed from a joint strong and weak lensing analsyis (SaWLens: Merten, J. et al. 2009, A&A, 500, 681) of combined Hubble and Subaru observations (Umetsu, K. et al. 2012, ApJ, 755, 56). The field is 24 arcminutes × 24 arcminutes in size (8.1Mpc at the cluster redshift). Lower right: A zoom in view of the boxed region in the left panel, with a side length of 8 arcminutes (2.7Mpc).
Abell 1689, a rich cluster at a redshift of z=0.183, is among the best studied galaxy clusters and one of the most powerful known lenses on the sky, characterized by a large Einstein radius of 47 arcseconds (for a reference source at z=2). This indicates an exceptionally high degree of mass concentration in projection of the cluster (Umetsu, K. & Broadhurst, T. 2008, ApJ, 684, 177). As such, Abell 1689 is known as a superlens cluster.
In a parametric triaxial framework, we have studied the intrinsic three-dimensional structure and geometry of the matter and gas distributions in Abell 1689, by performing a joint analysis of weak/strong lensing and X-ray/Sunyaev-Zel'dovich (SZ) effect data with minimal geometric assumptions (Umetsu, K. et al. 2015, ApJ, 806, 207). This multi-probe analysis uses Subaru telescope (weak-lensing shear and magnification), HST (strong lensing), XMM-Newton (X-ray), BIMA, OVRO, and SZA (thermal SZ effect) observations.
We have shown that the data favor an ellipsoidal, triaxial geometry with minor-major axis ratio 0.39 ± 0.15 and major axis closely aligned with the line of sight (22° ± 10°). This aligned orientation boosts the projected surface mass density and thus explains the exceptional high lensing strength of the cluster. We obtain a halo concentration c200c = 8.4 ± 1.3 at M200c = (1.7 ± 0.3) 10^15 solar masses, which overlaps with the > 1σ tail of the predicted probability distribution. That is, the cluster has a relatively high concentration but is not over-concentrated. The shape of the gas is found to be rounder than the underlying matter but quite elongated with minor-major axis ratio 0.60 ± 0.14. The gas mass fraction within 0.9Mpc is fgas = 10% (+2%, -3%), a typical value observed for high-mass clusters.
Lower: Mass distribution (white contours) of Abell 1689 overlaid on the Subaru BVRiz composite color image (Umetsu, K. et al. 2015, ApJ, 806, 207). The cluster mass distribution on large scales (> 1 arcminute) is reconstructed from a joint weak-lensing shear and magnification analysis of wide-field Subaru observations. The image is 30 arcminutes × 30 arcminutes in size (5.5Mpc at the cluster redshift).
My representative CLASH papers include
CLASH (P.I. Marc Postman, STScI) is a 524 orbit Hubble Space Telescope (HST) Multi-Cycle Treasury program that has been designed to probe the mass distribution of 25 high-mass clusters of galaxies using their gravitational lensing properties and to place new constraints on the fundamental components of the universe (Postman, M. et al. 2012, ApJS, 199, 25).
The CLASH program has observed these 25 clusters with HST over a 2.7 year period (November 2010 - July 2013). All its HST data were immediately released for public access. High-level data products (reduced images, catalogs, and models) of the HST and supporting Subaru observations are available at the MAST archive. IR data and catalogs from Spitzer and submillimeter data from Bolocam are both archived at IRSA (Bolocam, Spitzer).
Lower: Ensemble-averaged projected mass density profile Σ(R) (black squares) of the X-ray-selected CLASH subsample (gray curves) as a function of clustercentric radius R, obtained from a joint analysis of strong-lensing, weak-lensing shear and magnification data (Umetsu, K. et al. 2016, ApJ, 821, 116). The averaged mass profile is well described by a family of density profiles predicted for DM-dominated halos in gravitational equilibrium, namely, the Navarro-Frenk-White (NFW; cyan), Einasto, and DARKexp models. Cuspy halo models (red) that include the contribution from surrounding large scale structure provide improved agreement with the data.
My research interests and experience encompass the fields of observational cosmology and astrophysics, with the goal of understanding the nature of dark matter and its role in cosmic structure formation. To this end, my research is centered on galaxy clusters, the largest class of objects formed in the universe, and their surrounding large scale structure.
Massive galaxy clusters contain a wealth of cosmological information about the initial conditions of primordial density fluctuations, the emergence and growth of structure over cosmic time, thereby providing fundamental constraints on the unknown nature of dark matter (DM). In this framework, my research is primarily concerned with gravitational lensing effects, whereby the propagation of light rays is deflected as they travel through the expanding universe. Cluster gravitational lensing is a direct probe of the cosmic matter distribution dominated by invisible DM, and is also sensitive to the imprint of dark energy, thus offering a direct way to explore the dark side of the universe.
Lower left: Large scale structure of DM (62.5Mpc/h) in N-body simulations (Diemer, B. & Kravtsov, A.V. 2014, ApJ, 789, 1). Lower right: DM distribution (15Mpc/h) in and around a cluster-sized halo from N-body simulations (Diemer, B. & Kravtsov, A.V. 2014, ApJ, 789, 1). As seen in the left panel, cluster halos are located at dense nodes where the filaments intersect, generally triaxial reflecting the collisionless nature of DM, and elongated in the preferential infall directionof subhalos, namely, along surrounding filaments.
Figure credit: Diemer, B. & Mansfield, P.
Multi-probe 3D Analysis of the Superlens Cluster Abell 1689
RESEARCH HIGHLIGHTS
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