Weak lensing low multipoles

Journal article

We analyse the low-multipole components of the weak lensing convergence field in a Friedmann–Lemaître–Robertson–Walker (FLRW) universe. The low-multipole convergence field encodes the largest angle coherent potential gradients, essential for the assessment of large-angle features in data. To study this large-angle signal, we perform a combined analytical, numerical, and observational study. Starting from exact analytical expressions for the convergence power spectrum, we quantify how the dipole, quadrupole, and octupole build up with source redshift and show that, in cold dark matter (CDM), they saturate at an amplitude of order . We then use full-sky, horizon-scale N-body simulations (quijote) to explore the dependence of this signal on the observer’s environment, comparing random observers to ‘Milky Way-like’ observers. In parallel, we reconstruct the convergence field due to our local Universe with the 2MASS (Two Micron All-Sky Survey) Redshift Survey, with proper treatment of incompleteness and galaxy bias. We find that the observed low multipoles from observation are above the CDM mean predictions, but in full agreement with Milky Way-like observers in the simulation. Finally, by converting the convergence dipole into a number count dipole, we test whether weak lensing can contribute to the cosmic dipole anomaly, an idea motivated by its natural alignment with the CMB (cosmic microwave background) dipole and by the fact that lensing, unlike clustering, cannot be removed by cross-matching surveys and thus survives in all high-redshift catalogues. We show that weak lensing by local structure contributes at most a few per cent to this observed anomaly.

Authors: Bonnefous, A; Mohayaee, R

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Oxford University Press
• Journal: Monthly Notices of the Royal Astronomical Society
• Volume: 548
• Issue: 2
• Article number: stag633
• Publication date: 2026-04-02
• Acceptance date: 2026-03-24
• DOI: 10.1093/mnras/stag633
• EISSN: 1365-2966
• ISSN: 0035-8711
• Language: English
• Keywords: large-scale structure of Universe; cosmology: observations; gravitational lensing: weak