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Register a new userStrong and weak lensing united III: Measuring the mass distribution of the merging galaxy cluster 1E0657-56
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Marusa Bradac
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The galaxy cluster 1E0657-56 (z = 0.296) is remarkably well-suited for addressing outstanding issues in both galaxy evolution and fundamental physics. We present a reconstruction of the mass distribution from both strong and weak gravitational lensing data. Multi-color, high-resolution HST ACS images allow detection of many more arc candidates than were previously known, especially around the subcluster. Using the known redshift of one of the multiply imaged systems, we determine the remaining source redshifts using the predictive power of the strong lens model. Combining this information with shape measurements of weakly lensed sources, we derive a high-resolution, absolutely-calibrated mass map, using no assumptions regarding the physical properties of the underlying cluster potential. This map provides the best available quantification of the total mass of the central part of the cluster. We also confirm the result from Clowe et al. (2004,2006a).
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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.
We have shown that the cluster-mass reconstruction method which combines strong and weak gravitational lensing data, developed in the first paper in the series, successfully reconstructs the mass distribution of a simulated cluster. In this paper we apply the method to the ground-based high-quality multi-colour data of RX J1347.5-1145, the most X-ray luminous cluster to date. A new analysis of the cluster core on very deep, multi-colour data analysis of VLT/FORS data reveals many more arc candidates than previously known for this cluster. The combined strong and weak lensing reconstruction confirms that the cluster is indeed very massive. If the redshift and identification of the multiple-image system as well as the redshift estimates of the source galaxies used for weak lensing are correct, we determine the enclosed cluster mass in a cylinder to M(<360 h^-1 kpc)= (1.2 +/- 0.3) 10^15 Msun. In addition the reconstructed mass distribution follows the distribution found with independent methods (X-ray measurements, SZ). With higher resolution (e.g. HST imaging data) more reliable multiple imaging information can be obtained and the reconstruction can be improved to accuracies greater than what is currently possible with weak and strong lensing techniques.
In the hierarchical structure formation model of the universe, galaxy clusters are assembled through a series of mergers. Accordingly, it is expected that galaxy clusters in the early universe are actively forming and dynamically young. Located at a high redshift of z=1.71, SpARCS1049+56 offers a unique look into the galaxy cluster formation process. This cluster has been shown to be rich in cluster galaxies and to have intense star formation. Its high redshift pushes a weak-lensing analysis beyond the regime of the optical spectrum into that of the infrared. Equipped with deep Hubble Space Telescope Wide Field Camera 3 UVIS and IR observations, we present a weak-lensing characterization of SpARCS1049+56. As few IR weak-lensing studies have been performed, we discuss the details of PSF modeling and galaxy shape measurement for an IR weak-lensing procedure and the systematics that come with the territory. It will be critical to understand these systematics in future weak-lensing studies in the IR with the next generation space telescopes such as JWST, Euclid, and WFIRST. Through a careful analysis, the mass distribution of this young galaxy cluster is mapped and the convergence peak is detected at a 3.3 sigma level. The weak-lensing mass of the cluster is estimated to be $3.5pm1.2times10^{14} text{M}_odot$ and is consistent with the mass derived from a mass-richness scaling relation. This mass is extreme for a cluster at such a high redshift and suggests that SpARCS1049+56 is rare in the standard $Lambda$CDM universe.
After a brief introduction to gravitational lensing theory, a rough overview of the types of gravitational lensing statistics that have been performed so far will be given. I shall then concentrate on recent results of galaxy-galaxy lensing, which indicate that galactic halos extend much further than can be probed via rotation of stars and gas.
We present a weak-lensing analysis of the merging {em Frontier Fields} (FF) cluster Abell~2744 using new Subaru/Suprime-Cam imaging. The wide-field lensing mass distribution reveals this cluster is comprised of four distinct substructures. Simultaneously modeling the two-dimensional reduced shear field using a combination of a Navarro--Frenk--White (NFW) model for the main core and truncated NFW models for the subhalos, we determine their masses and locations. The total mass of the system is constrained as $M_mathrm{200c} = (2.06pm0.42)times10^{15},M_odot$. The most massive clump is the southern component with $M_mathrm{200c} = (7.7pm3.4)times10^{14},M_odot$, followed by the western substructure ($M_mathrm{200c} = (4.5pm2.0)times10^{14},M_odot$) and two smaller substructures to the northeast ($M_mathrm{200c} = (2.8pm1.6)times10^{14},M_odot$) and northwest ($M_mathrm{200c} = (1.9pm1.2)times10^{14},M_odot$). The presence of the four substructures supports the picture of multiple mergers. Using a composite of hydrodynamical binary simulations we explain this complicated system without the need for a slingshot effect to produce the northwest X-ray interloper, as previously proposed. The locations of the substructures appear to be offset from both the gas ($87^{+34}_{-28}$ arcsec, 90% CL) and the galaxies ($72^{+34}_{-53}$ arcsec, 90% CL) in the case of the northwestern and western subhalos. To confirm or refute these findings, high resolution space-based observations extending beyond the current FF limited coverage to the west and northwestern area are essential.
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