An ultra-high-resolution map of (dark) matter

Abstract

Ordinary matter-including particles such as protons and neutrons-accounts for only about one sixth of all matter in the Universe. The rest is dark matter, which does not emit or absorb light but plays a fundamental role in galaxy and structure evolution. Because it interacts only through gravity, one of the most direct probes is weak gravitational lensing: the deflection of light from distant galaxies by intervening mass. Here we present an extremely detailed, wide-area weak-lensing mass map, covering 0.77 deg x 0.70 deg, using high-resolution imaging from the James Webb Space Telescope (JWST) as part of the COSMOS-Web survey. By measuring the shapes of 129 galaxies per square arcminute-many independently in the F115W and F150W bands-we achieve an angular resolution of 1.00 +/- 0.01 arcmin. Our map has more than twice the resolution of earlier Hubble Space Telescope maps, revealing how dark and luminous matter co-evolve across filaments, clusters, and under-densities. It traces mass features out to z ~ 2, including the most distant structure at z ~ 1.1. The sensitivity to high-redshift lensing constrains galaxy environments at the peak of cosmic star formation and sets a high-resolution benchmark for testing theories about the nature of dark matter and the formation of large-scale cosmic structure

Figures (5)

• Figure 1: Map of cosmic structure, from measurements of weak gravitational lensing with JWST and HST. Colours show the $E$-mode convergence ($\kappa$), where positive (blue) regions indicate mass overdensities and negative (brown) regions represent underdensities along the line of sight. The central region, outlined in red, corresponds to the COSMOS-Web footprint observed with JWST at a spatial resolution of $\sigma=1.0$ arcmin. It is embedded within a wider HST-based map at $\sigma=2.4$ arcmin resolution, to reduce edge effects and highlight the enhanced resolving power of JWST.
• Figure 2: Sensitivity of weak lensing to mass at different cosmic distances, quantified by redshift, $z$. a, Dashed lines show the measured number density, $n(z)$ of galaxies whose shapes, distorted by lensing, are resolved by JWST, HST, and HSC, in bins of width $\Delta z = 0.04$. JWST resolves the shapes of progressively more distant galaxies than other telescopes. Solid lines show the implied sensitivity functions $g(z)$ to foreground mass. b, Ratio of the JWST lensing sensitivity to that of HSC and HST. JWST has higher sensitivity at all redshifts, but especially at high redshift.
• Figure 3: Measured shear distortion of distant galaxies. The shapes of all galaxies from F115W and F150W-band imaging are averaged in $1.1'\times 1.1'$ pixels, followed by denoising through smoothing with a Gaussian filter of width $\sigma=1.2$ arcmin. The white line segments depict the local amplitude and orientation of the shear. The background image shows the signal-to-noise ratio, S/N$_{\mathrm{WL}}$, of the amplitude of the "curl-free $E$-mode" component of this pseudo-vector field. The reference bar in the top-right corner corresponds to $\gamma=0.05$ (5% distortion relative to unlensed shapes).
• Figure 4: Maps of the weak gravitational lensing convergence from JWST and HST. a, JWST-based $E$-mode convergence map, showing the projected distribution of mass. b, JWST $B$-mode (null test) convergence map, which could contain systematic biases but is more than an order of magnitude lower in amplitude. c, HST-based $E$-mode convergence map, cropped to the JWST COSMOS-Web footprint, illustrating the same field at lower resolution Massey2007_Nature. In all panels, the colour scale is identical, with brighter tones indicating mass overdensities, and an in-painting technique is applied to handle masked regions.
• Figure 5: Maps of weak gravitational lensing, X-ray emission, and galaxy density in the COSMOS field. a–c, Combined JWST (red square; F115W+F150W) and HST (surrounding area) weak lensing convergence map ($\kappa$), with contours at $\kappa=0.004$ and uniformly spaced by $\Delta\kappa=0.005$, matching the levels used in Massey2007_Nature for direct comparison. Dashed sections mark the negative portions of the contours, corresponding to the same first convergence levels. a, Green triangles represent galaxy clusters newly detected in the JWST mass map, while orange crosses indicate clusters detected in both JWST and HST maps and matching known systems from XMM-Newton and Chandra, whose mass and redshift mean they should be (and are) detected at S/N$_\mathrm{det}>3$ in weak lensing. b, X-ray emission from hot gas in massive halos, traced with data from XMM-Newton and Chandra, with overlaid white $\kappa$ contours. c, Galaxy overdensity significance map ($\Sigma/\sigma$), weighted by the weak lensing sensitivity function $g(z)$, tracing the projected distribution of luminous matter, with white $\kappa$ contours marking the total mass.