2025ApJ...993L..50U

We present a study of the metal, dust, and molecular gas content in galaxies within the A2744-z7p9OD protocluster at z ≈ 7.88. We focus on two galaxy groups-the Quintet and the Chain-which are covered by the Emission-Line Protocluster Imaging Survey (ELPIS) of the furthest overdensity beyond Pandora's Cluster A2744. [C II] 158 μm emission is detected in five galaxies, revealing molecular gas reservoirs with ${\rm{log}}({M}_{{\rm{gas}}}/{M}_{\odot })\sim 9.0$-9.6, while dust continuum at the observed frame of 1.26 mm is detected in three galaxies, yielding dust masses of ${\rm{log}}({M}_{{\rm{dust}}}/{M}_{\odot })\sim 6.0$-6.4, assuming a dust temperature of ${T}_{{\rm{dust}}}=4{5}_{-15}^{+15}$ K. The derived properties-including stellar-to-dust mass ratios of $\mathrm{log}({M}_{{\rm{dust}}}/{M}_{\star })\sim -3$ to -2 at $\mathrm{log}({M}_{\star }/{M}_{\odot })\approx 9$ and dust-to-gas mass ratios of $\mathrm{log}({M}_{{\rm{dust}}}/{M}_{{\rm{gas}}})\sim -4$ to -3 at $12+\mathrm{log}({\rm{O}}/{\rm{H}})\approx 8$-place these galaxies in an intermediate regime: higher than the very low ratios expected from supernova-driven dust production but still below the levels attained once efficient grain growth dominates. These values indicate a transition phase of dust mass assembly, likely reflecting the onset of grain growth via metal accretion under accelerated evolution in the protocluster core.