COSMOS-z3.1-A maps a distant massive structure in three dimensions
Narrowband imaging and spectra from Keck, Gemini and DESI reconstructed COSMOS-z3.1-A in three dimensions at redshift 3.1. NOIRLab and Purdue University report that the ten-peak proto-supercluster is seen when the Universe was 2.1 billion years old, while its apparent shape remains sensitive to viewing direction.
Science··Morning
A two-dimensional overdensity gained depth
The ODIN survey selected dense galaxy concentrations at redshift 3.1 in the COSMOS field with narrowband imaging. The team followed the candidates with spectra from Keck, Gemini and DESI, adding distance information to reconstruct COSMOS-z3.1-A and a second complex in three dimensions across roughly 50 comoving megaparsecs. NOIRLab and Purdue University report the same study. COSMOS-z3.1-A is described as the earliest proto-supercluster, seen when the Universe was 2.1 billion years old.[1], [2]
Ten peaks, not one cluster
The reconstruction finds ten distinct density peaks within COSMOS-z3.1-A and four in the second complex. The structures are clumpy, elongated along one axis and located where several cosmic-web filaments converge. That arrangement is consistent with hierarchical models in which smaller structures form first and later merge into massive clusters. The estimated total mass is about 5,000 times that of the Milky Way. This is not a direct weighing; it is a model-based descendant-mass estimate from the observed galaxy overdensities.[1], [2]
Viewing direction changes the shape
A key limitation is the elongated structure's orientation relative to the observer. The team says its probabilistic reconstruction, tested with simulations, outperforms approaches based on spectroscopy alone; even so, elongation along one axis means a sky projection can make the true three-dimensional structure appear more compact or diffuse. The study has been accepted by The Astrophysical Journal, and an arXiv version appeared earlier. It provides a strong example of early large-structure formation, but one object does not discriminate among all cosmological models.[1], [2]
