Joint JWST-DECam Lensing Reveals That the Bullet Cluster Is a Minor Merger

TL;DR

This study uses advanced joint lensing analysis with JWST and DECam data to accurately determine the Bullet Cluster's mass ratio, revealing it as a minor merger and resolving previous discrepancies.

Contribution

It introduces a robust joint weak+strong lensing method combining JWST and DECam data to precisely measure the Bullet Cluster's mass components.

Findings

The Bullet Cluster's mass ratio is approximately 10:1, classifying it as a minor merger.

Resolved three distinct halos using JWST's high-quality data.

Eliminated the need for extrapolation with wide-field DECam coverage.

Abstract

We present the first robust virial masses of the Bullet Cluster's three individual components from a joint weak+strong lensing analysis combining JWST/NIRCam and DECam observations. Despite its status as the benchmark system for dark matter and merger studies, inferred mass ratios for the Bullet Cluster have spanned a wide range from $\sim$2:1 to $\gtrsim$10:1 over more than two decades. We revisit this tension through three key advances: (1) JWST's exceptional data quality enables us to resolve three distinct halos, (2) DECam's wide-field coverage beyond its virial radius eliminates the need for extrapolation, and (3) high-fidelity strong-lensing priors mitigate weak-lensing model bias. We obtain $M_{200c} = 15.11^{+2.48}_{-2.10} \times 10^{14}M_{\odot}$ for the main cluster and $1.49^{+0.32}_{-0.25} \times 10^{14}M_{\odot}$ for the subcluster, yielding a mass ratio of $10.14^{+3.22}_{-2.47}$, definitively classifying the Bullet Cluster as a minor merger. This result reconciles the long-standing tension in the mass ratio and provides updated initial parameters for future modeling of this iconic system.