Frontier Fields: Subaru Weak-Lensing Analysis of the Merging Galaxy Cluster A2744*

Abstract

We present a weak-lensing analysis of the merging 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 200c = (2.06 ± 0.42) × 10 15 M . The most massive clump is the southern component with M 200c = (7.7 ± 3.4) × 10 14 M , followed by the western substructure (M 200c = (4.5 ± 2.0) × 10 14 M ) and two smaller substructures to the northeast (M 200c = (2.8 ± 1.6) × 10 14 M ) and northwest (M 200c = (1.9 ± 1.2) × 10 14 M ). 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.

VLA Radio Observations of the HST Frontier Fields Cluster Abell 2744: The Discovery of New Radio Relics

“…Finally, we identify a patch of diffuse emission north of the radio halo (labelled R4 in It covers a much smaller area than the other diffuse sources (50 × 30 kpc 2 ). We do not find an optical counterpart to the source in the images from Medezinski et al (2016).…”

“…The relatively bright compact source at R. A.=3°. 4999688, decl.=−30°.3459524 has =  z 0.46 phot 0.05 (Medezinski et al 2016) and is thus likely a background object and not associated with R3.…”

“…One compact radio source is embedded within R1-A (R.A.=3°. 6538408, decl.=−30°.3296082), but this seems to be a background source with =  z 0.59 0.07 phot (Medezinski et al 2016). The observed mean polarization fraction of 27% of R1 is typical for radio relics and suggests a high degree of ordering of the magnetic fields (B), aligning them within the shock plane (e.g., Clarke & Enßlin 2006;Bonafede et al 2009).…”

“…Optical, X-ray, and radio overlay of A2744. The Subaru optical BRz color image comes from Medezinski et al (2016). The Chandra 0.5-2.0keV image is shown in blue.…”

“…More recently, a weak-lensing analysis of A2744 was conducted by Medezinski et al (2016) using new Subaru/Suprime-Cam images. They identified four substructures similar to those of Merten et al (2011) but determined a much reduced mass for the northern core, and instead identified a more prominent northeastern core.…”