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

Joint JWST-DECam Lensing Reveals That the Bullet Cluster Is a Minor Merger
Boseong Young Cho, M. James Jee, Hyungjin Joo, Sangjun Cha, Kim HyeongHan
arXiv:2512.03150v1 Announce Type: new
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.arXiv:2512.03150v1 Announce Type: new
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.