We report the discovery of a large-scale structure containing multiple overdensities at z= 4. 54 0. 03 in the COSMOS field, with the most prominent one likely infalling towards the recently identified Taralay protocluster. We use combined wide-band and narrow-band optical photometry to identify Lyα emitters (LAEs) within a 21 cMpc radius from the submm source J1000+0234, at z= 4. 54, to identify typical star-forming galaxies that may trace an underlying structure. Our approach selects line emitters as narrow-band excess objects and we use the COSMOS2020 photometric redshift catalog to eliminate potential low-redshift interlopers whose line emission (e. g. OIII at z 0. 3) might be responsible for the observed excess in the narrow band. In comparison with the LAE density in the field, our results point to a mean LAE number overdensity of δ= 3 spanning a region of 27 20 36 cMpc³, probably evolving into a moderate-mass cluster (3 - 10 10^14 \, M_) at z 0. This work supports the idea that submm sources, although offset from the major overdensity peaks, serve as traces of moderately massive, potentially infalling structures.
Rubet et al. (Tue,) studied this question.