Kinematic Decomposition of the BCG and ICL in Abell S1063 and MACS J1206
Abstract
The brightest cluster galaxy (BCG) and the intracluster light (ICL) overlap in space and merge smoothly in surface brightness. Beyond the nearest clusters, measurements of the ICL have therefore relied on photometric definitions. We present a spectral decomposition of the light in cluster cores into BCG and ICL, using deep VLT/MUSE integral-field spectroscopy of Abell S1063 (z=0.35) and MACS J1206.2−0847 (z=0.44). Spectral templates of the two components are derived iteratively from the BCG center and the ICL-dominated outskirts, and their weighted sum is fitted to the spectrum of every spatial bin. This enables us to measure the kinematics and the light of the BCG and ICL separately without assuming a boundary or a functional form for their light profiles. The velocity dispersions of the BCG and ICL are 316±5 and 753±25 km s−1, respectively, in AS1063, whereas we obtain 313±5 and 695+47−45 km s−1 in MACS1206. The ICL is blueshifted relative to the BCG by 75±22 and 148±38 km s−1, respectively, and is ~0.7 dex more metal-poor, at a combined statistical significance of ~2σ. Defining the ICL as the light fainter than μB=25 mag arcsec−2 assigns two-thirds to three-quarters of the kinematically defined ICL to the BCG, while a double Sersic model fits the total profiles well but leaves the division between the two components poorly constrained given the depth and resolution of the current MUSE data. Our kinematic decomposition provides a direct, physically motivated reference for photometric definitions of the ICL.
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BibTeX
@misc{joo2026kinematic,
title = {{Kinematic Decomposition of the BCG and ICL in Abell S1063 and MACS J1206}},
author = {Hyungjin Joo and Myungkook James Jee},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.40792},
eprint = {2610.40792},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.40792},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Kinematic Decomposition of the BCG and ICL in Abell S1063 and MACS J1206
AU - Hyungjin Joo
AU - Myungkook James Jee
PY - 2026
DA - 2026/10/29
PB - arXiv
DO - 10.48550/arxiv.2610.40792
UR - https://arxiv.org/abs/2610.40792
AB - The brightest cluster galaxy (BCG) and the intracluster light (ICL) overlap in space and merge smoothly in surface brightness. Beyond the nearest clusters, measurements of the ICL have therefore relied on photometric definitions. We present a spectral decomposition of the light in cluster cores into BCG and ICL, using deep VLT/MUSE integral-field spectroscopy of Abell S1063 (z=0.35) and MACS J1206.2−0847 (z=0.44). Spectral templates of the two components are derived iteratively from the BCG center and the ICL-dominated outskirts, and their weighted sum is fitted to the spectrum of every spatial bin. This enables us to measure the kinematics and the light of the BCG and ICL separately without assuming a boundary or a functional form for their light profiles. The velocity dispersions of the BCG and ICL are 316±5 and 753±25 km s^−1, respectively, in AS1063, whereas we obtain 313±5 and 695^+47_−45 km s^−1 in MACS1206. The ICL is blueshifted relative to the BCG by 75±22 and 148±38 km s^−1, respectively, and is ~0.7 dex more metal-poor, at a combined statistical significance of ~2σ. Defining the ICL as the light fainter than μ_B=25 mag arcsec^−2 assigns two-thirds to three-quarters of the kinematically defined ICL to the BCG, while a double Sersic model fits the total profiles well but leaves the division between the two components poorly constrained given the depth and resolution of the current MUSE data. Our kinematic decomposition provides a direct, physically motivated reference for photometric definitions of the ICL.
ER -