The Distribution of Dark and Luminous Matter in the Unique Galaxy
  Cluster Merger Abell 2146
  Abell 2146 ($z$ = 0.232) consists of two galaxy clusters undergoing a major
merger. The system was discovered in previous work, where two large shock
fronts were detected using the $\textit{Chandra X-ray Observatory}$, consistent
with a merger close to the plane of the sky, caught soon after first core
passage. A weak gravitational lensing analysis of the total gravitating mass in
the system, using the distorted shapes of distant galaxies seen with ACS-WFC on
$\textit{Hubble Space Telescope}$, is presented. The highest peak in the
reconstruction of the projected mass is centred on the Brightest Cluster Galaxy
(BCG) in Abell 2146-A. The mass associated with Abell 2146-B is more extended.
Bootstrapped noise mass reconstructions show the mass peak in Abell 2146-A to
be consistently centred on the BCG. Previous work showed that BCG-A appears to
lag behind an X-ray cool core; although the peak of the mass reconstruction is
centred on the BCG, it is also consistent with the X-ray peak given the
resolution of the weak lensing mass map. The best-fit mass model with two
components centred on the BCGs yields $M_{200}$ =
1.1$^{+0.3}_{-0.4}$$\times$10$^{15}$M$_{\odot}$ and
3$^{+1}_{-2}$$\times$10$^{14}$M$_{\odot}$ for Abell 2146-A and Abell 2146-B
respectively, assuming a mass concentration parameter of $c=3.5$ for each
cluster. From the weak lensing analysis, Abell 2146-A is the primary halo
component, and the origin of the apparent discrepancy with the X-ray analysis
where Abell 2146-B is the primary halo is being assessed using simulations of
the merger.
