A filament of dark matter between two clusters of galaxies

TL;DR

This paper reports the first direct detection of a dark matter filament connecting galaxy clusters using weak gravitational lensing, confirming a key prediction of the cosmic web structure in the universe.

Contribution

The study provides the first direct observational evidence of a dark matter filament via weak lensing, linking it with galaxy overdensities and X-ray emission in a supercluster.

Findings

Detected a dark matter filament connecting galaxy clusters.

The filament's mass is comparable to an additional galaxy cluster.

Placed an upper limit of 0.09 on the hot gas fraction in the filament.

Abstract

It is a firm prediction of the concordance Cold Dark Matter (CDM) cosmological model that galaxy clusters live at the intersection of large-scale structure filaments. The thread-like structure of this "cosmic web" has been traced by galaxy redshift surveys for decades. More recently the Warm-Hot Intergalactic Medium (WHIM) residing in low redshift filaments has been observed in emission and absorption. However, a reliable direct detection of the underlying Dark Matter skeleton, which should contain more than half of all matter, remained elusive, as earlier candidates for such detections were either falsified or suffered from low signal-to-noise ratios and unphysical misalignements of dark and luminous matter. Here we report the detection of a dark matter filament connecting the two main components of the Abell 222/223 supercluster system from its weak gravitational lensing signal, both in a non-parametric mass reconstruction and in parametric model fits. This filament is coincident with an overdensity of galaxies and diffuse, soft X-ray emission and contributes mass comparable to that of an additional galaxy cluster to the total mass of the supercluster. Combined with X-ray observations, we place an upper limit of 0.09 on the hot gas fraction, the mass of X-ray emitting gas divided by the total mass, in the filament.