Deep view of the intracluster light in the Coma cluster of galaxies

The detection and study of the intracluster light (ICL) in rich clusters of galaxies has been a longstanding challenge and key focus. Using the lowest-surface-brightness images of the Coma cluster of galaxies in the g and r bands, from the Halos and Environment of Nearby Galaxies (HERON) Coma Cluster Project, we obtained the most extensive image of ICL in a single cluster to date, spreading over 1.5 Mpc from the cluster core. The unprecedented wealth of spectroscopic data from the Dark Energy Spectroscopic Instrument (DESI) Early Data Release, along with a compilation from the NASA/IPAC Extragalactic Database and available data from the literature, enabled the identification of 2157 galaxy members within Coma; on this basis, 42 distinct groups were identified. The synergy between these high-quality data allowed us to: (1) calculate ICL fractions of 19.9 ± 0.5% and 19.6 ± 0.6% in the g and r bands, respectively, consistent with a dynamically active cluster; (2) unveil Coma’s faintest tidal features; and (3) provide a comprehensive picture of the dynamics and interactions within this complex system. Our findings indicate that the ICL connects several of these groups in a filamentous network, from which we can infer ongoing dynamical processes. In particular, we identified a faint stellar bridge linking the core of Coma with the galaxy NGC 4839, providing compelling evidence that this galaxy has already traversed the central region of the cluster.