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

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 (M_{12, 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 10^{3 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.}}