SLICE: Unveiling the Multi-Component Merging Core of SPT-CLJ1150-2805 Through Strong-Lensing Mass Modelling
Abstract
We present a new strong-lensing and X-ray mass model of the merging galaxy cluster SPT-CLJ1150-2805 (z=0.383), combining JWST NIRCam, HST, Chandra, and VLT/MUSE data to robustly decompose its collisionless and collisional components. Exploiting JWST, we expand the multiple-image catalogue with 66 new images (30 comprising 6 new systems). Our baseline model uses 118 spectroscopically confirmed images from 20 systems, achieving an image-plane root-mean-square offset of 0.56''. An expanded model incorporating 31 additional photometric images from 8 additional systems yields a near-identical mass distribution, confirming excellent model stability. We resolve a complex multi-axis post-merger system requiring five cluster-scale dark matter haloes, including a bimodal core with distinct haloes coincident with each brightest cluster galaxy. The remaining mass components are independently supported by kinematics of 291 cluster members (σv=1960+84−92 km s−1), which reveal two new galaxy substructures - the northernmost of which we tentatively identify as the baryonic counterpart to our fifth dark matter halo. The cluster is an extraordinarily efficient lens, possessing an effective Einstein radius θE=42.41+0.05−0.04'' and an enclosed mass M(<θE)=3.35+0.04−0.03×1014M⊙ for a source at zs=2. For a high-redshift source at zs=9, it produces a magnification cross-section of A(>10)≃0.15 arcmin2 and A(>30)≃0.020 arcmin2. This global lensing power surpasses all Hubble Frontier Fields clusters. In a regime where systematic uncertainties between mass models dominate high-redshift magnification errors, the stability of our reconstruction sets this lens apart. This combination of extreme lensing power and a robust mass model establishes SPT-CLJ1150-2805 as a premier cosmic telescope for high-redshift studies.
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BibTeX
@misc{betts2026slice,
title = {{SLICE: Unveiling the Multi-Component Merging Core of SPT-CLJ1150-2805 Through Strong-Lensing Mass Modelling}},
author = {James R Betts and Benjamin Beauchesne and Mathilde Jauzac and David Lagattuta and Guillaume Mahler and Jean-Paul Kneib and Gavin Leroy and Marceau Limousin and Priyamvada Natarajan and Sameeksha Saini and Keren Sharon and Stephane V Werner and Catherine Cerny and Isaque Dutra and Dominique Eckert and Alaina Einsig and Michael D Gladders and Gourav Khullarm and Manon Regamey},
howpublished = {HAL},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.31944},
eprint = {2609.31944},
archivePrefix = {arXiv},
url = {https://hal.science/hal-05830217v1},
}
RIS
TY - UNPB
TI - SLICE: Unveiling the Multi-Component Merging Core of SPT-CLJ1150-2805 Through Strong-Lensing Mass Modelling
AU - James R Betts
AU - Benjamin Beauchesne
AU - Mathilde Jauzac
AU - David Lagattuta
AU - Guillaume Mahler
AU - Jean-Paul Kneib
AU - Gavin Leroy
AU - Marceau Limousin
AU - Priyamvada Natarajan
AU - Sameeksha Saini
AU - Keren Sharon
AU - Stephane V Werner
AU - Catherine Cerny
AU - Isaque Dutra
AU - Dominique Eckert
AU - Alaina Einsig
AU - Michael D Gladders
AU - Gourav Khullarm
AU - Manon Regamey
PY - 2026
DA - 2026/09/25
PB - HAL
DO - 10.48550/arxiv.2609.31944
UR - https://hal.science/hal-05830217v1
AB - We present a new strong-lensing and X-ray mass model of the merging galaxy cluster SPT-CLJ1150-2805 (z=0.383), combining JWST NIRCam, HST, Chandra, and VLT/MUSE data to robustly decompose its collisionless and collisional components. Exploiting JWST, we expand the multiple-image catalogue with 66 new images (30 comprising 6 new systems). Our baseline model uses 118 spectroscopically confirmed images from 20 systems, achieving an image-plane root-mean-square offset of 0.56''. An expanded model incorporating 31 additional photometric images from 8 additional systems yields a near-identical mass distribution, confirming excellent model stability. We resolve a complex multi-axis post-merger system requiring five cluster-scale dark matter haloes, including a bimodal core with distinct haloes coincident with each brightest cluster galaxy. The remaining mass components are independently supported by kinematics of 291 cluster members (σ_v=1960^+84_−92 km s^−1), which reveal two new galaxy substructures - the northernmost of which we tentatively identify as the baryonic counterpart to our fifth dark matter halo. The cluster is an extraordinarily efficient lens, possessing an effective Einstein radius θ_E=42.41^+0.05_−0.04'' and an enclosed mass M(<θ_E)=3.35^+0.04_−0.03×10^14M_⊙ for a source at z_s=2. For a high-redshift source at z_s=9, it produces a magnification cross-section of A(>10)≃0.15 arcmin^2 and A(>30)≃0.020 arcmin^2. This global lensing power surpasses all Hubble Frontier Fields clusters. In a regime where systematic uncertainties between mass models dominate high-redshift magnification errors, the stability of our reconstruction sets this lens apart. This combination of extreme lensing power and a robust mass model establishes SPT-CLJ1150-2805 as a premier cosmic telescope for high-redshift studies.
ER -