Cluster connectivity in DES Y3 data: impact on galaxy properties

Connectivity, namely the number of cosmic filaments reaching out of groups or clusters, has recently emerged as an informative way to quantify environment. The new analysis still awaits peer review, but it already lays out the central claim clearly.

This matters because cosmology operates at the edge of what current instruments can measure, where systematic errors and model assumptions are never trivial. Small discrepancies between independent measurements have historically pointed toward missing physics rather than simple calibration errors, and the ongoing tension in the Hubble constant is a live example of how a persistent disagreement between methods can reshape the theoretical landscape. Each new dataset that approaches this territory with independent systematics adds real information to a problem that has resisted easy resolution for more than a decade. With the advent of wide-area photometric surveys, it becomes possible to measure connectivity on a statistically significant sample of clusters. In this work, we extract the cosmic web from the DES Y3 photometric data and measure the connectivity around clusters from several public catalogs up to $z < 1$.

We first recover the well-established trend that cluster connectivity increases with cluster mass at all redshifts. We then investigate the properties of cluster member galaxies and find that, at fixed mass, clusters with a higher fraction of red (elliptical) galaxies are more strongly.

Furthermore, by examining the radial profiles of the red and elliptical galaxy fractions, we obtain hints that galaxy populations may undergo pre-processing within filamentary. Overall, we demonstrate that despite photometric redshift uncertainties and projection effects, our method allows for the quantification of the cosmic web environment around.

This work is consistent with results based on the Euclid Quick Release 1 (Q1). We plan to publicly release the cluster connectivity catalog as well as the cosmic filament catalog.

The relevance goes beyond one dataset because even small shifts in measured parameters can matter when the field is testing the limits of the standard cosmological model. The Lambda-CDM framework describes the observable universe with remarkable economy, but its success rests on two components, dark matter and dark energy, whose physical nature remains entirely unknown. Any credible measurement that tightens or loosens the constraints on those components moves the entire theoretical enterprise forward, regardless of whether the immediate result looks dramatic on its own terms.

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Because this is still a preprint, the result should be read with genuine interest and proportionate caution. Peer review is not a guarantee of correctness, but it is a process that forces authors to respond to technical criticism from specialists who have no stake in a particular outcome. Preprints that survive that process, often with substantive revisions, emerge with a stronger evidential base than the version that first appeared. Until that stage is complete, the responsible reading keeps uncertainty explicitly visible rather than treating the claims as established findings.

The next step is to see whether the effect survives when independent surveys, different calibration strategies and tighter control of systematic uncertainties enter the picture. Programmes such as Euclid, DESI and the Rubin Observatory will deliver datasets over the next several years that cover the same parameter space with largely independent methods. If the current signal persists through those tests, its theoretical implications will become impossible to set aside. Until peer review and independent follow-up address those open questions, skepticism is not a failure of appreciation for the work; it is part of how science decides what to keep.

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