Poster Presentation

Accurate Mass of the Bullet Cluster from a Joint Weak and Strong Lensing Analysis: Combined JWST and DECam Data without Extrapolation

Author(s): Boseong Cho (Yonsei University)

Presenter: Boseong Cho (Yonsei University, Seoul)

We present an accurate mass of the Bullet Cluster (1E 0657-56; z=0.296) using a combination of high-resolution JWST/NIRCam imaging and wide-field DECam data. Despite being a benchmark for cluster mergers and dark matter studies, fundamental uncertainties in its mass have prevented a consensus on whether it is a major or minor merger system. These uncertainties arise from critical observational limitations in previous virial mass estimates: studies with higher source density (~70 arcmin^{-2}) were severely limited to fields much smaller than R_{200}, while wide-field surveys extending to R_{200} had low source density (~10 arcmin^{-2}). Our analysis utilizes JWST's unprecedented depth with high weak lensing source density (~400 arcmin^{-2}) and DECam's extensive coverage out to ~5 x R_{200}. We model the system using Navarro-Frenk-White profiles without assuming mass-concentration relations, reducing model-dependent biases by anchoring the model with strong-lensing projected mass constraints around the cluster cores. This approach reveals a large mass ratio between the two primary components, definitively classifying the collision as a minor merger. This result provides crucial initial conditions for hydrodynamical simulations, significantly revising our understanding of this iconic cluster merger's formation history.