Multi-scale exploration of SMACS J0723.3–7327’s intracluster light and past dynamical history

OCA, P.H.C Boulevard de l’Observatoire CS 34229, 06304 Nice Cedex 4, France

^⋆ Corresponding author.

Received: 9 January 2025
Accepted: 1 April 2025

Abstract

We present an analysis of the intracluster light (ICL) in the galaxy cluster SMACS J0723.3–7327 (hereafter, SMACS J0723) using JWST/NIRCam deep imaging in six filters (F090W to F444W). We processed images for low surface brightness (LSB) science, applying additional corrections for instrumental scattering in the short-wavelength channels. We analysed the images using wavelet-based decomposition and extracted and modelled the ICL, brightest cluster galaxy (BCG), and satellite galaxies, generating 2D maps for each component. The ICL and ICL + BCG fractions, computed in all filters within a 400 kpc radius, exhibit a flat trend with wavelength, averaging 28% and 34%, respectively. Flux ratios between the BCG and the next brightest members (M₁₂, M₁₃, and M₁₄) also display minimal wavelength dependence. These results indicate that SMACS J0723 is a dynamically evolved cluster with a dominant BCG and well-developed ICL. We analysed five prominent ICL substructures that contribute 10–12% of the total ICL+BCG flux budget, slightly exceeding simulation predictions. Their short dynamical timescales suggest an instantaneous ICL injection rate of several 10³ L_⊙ yr⁻¹, consistent with active dynamical assembly. These findings support a scenario where SMACS J0723’s ICL growth is currently driven by galaxy mergers involving the BCG and other bright satellites, rather than by the accretion of pre-processed ICL from a recent cluster merger. However, extrapolating the current injection rate to the cluster’s lifetime indicates that additional mechanisms are required to match the growth observed in other clusters over cosmic timescales.