AtLAST -- Cosmology with submillimetre galaxies magnification bias

TL;DR

This work advocates magnification bias as a powerful, independent cosmological probe that uses foreground–background cross-correlations of high-redshift submillimetre galaxies to access galaxy–matter information without relying on shear measurements. It argues that a next-generation wide-field submm facility, AtLAST, is essential to overcome current limitations and unlock high-precision cosmology from magnification bias, including constraints on $\Omega_m$, $\sigma_8$, and dark-energy evolution characterized by $w_0$ and $w_a$, as well as neutrino-mass bounds. The paper projects that AtLAST could deliver order-of-magnitude improvements in parameter constraints through uniform, deep surveys, background tomography, and precise redshift/number-count characterisation, making magnification bias a cornerstone of precision cosmology in the 2030s. Overall, the study positions magnification bias as a robust cross-check and complementary probe to optical shear and CMB analyses, with significant implications for our understanding of dark energy, structure growth, and the high-redshift dusty universe.

Abstract

Magnification bias offers a uniquely powerful and independent route to cosmological information. As a gravitational-lensing observable, it probes galaxy-matter correlations without relying on galaxy shapes, PSF modelling, or intrinsic-alignment corrections. Its sensitivity spans both geometry and growth: magnification bias simultaneously responds to the matter density, the amplitude of structure, and the redshift evolution of dark energy (DE) below $z \leq 1$. Importantly, its parameter degeneracy directions differ from those of shear, Baryon Acoustic Oscillations (BAO), and Cosmic Microwave Background (CMB) data, making it a complementary and consistency-check probe with substantial diagnostic value for the next decade of precision cosmology. However, the current potential of magnification bias is restricted by limited sky coverage, catalogue inhomogeneities, and insufficiently precise redshift or number-count characterisation. A next-generation wide-field submillimetre facility like AtLAST -- capable of uniform, deep surveys and spectroscopic mapping -- would overcome these limitations and transform magnification bias into a competitive, high-precision cosmological tool.

Figures (2)

• Figure 1: Description of the Magnification Bias Effect
• Figure 1: Preliminary $w_0$-$\Omega_m$ posterior probability contours for different study cases with and without fixing $\Omega_m$. Data from other works are also plotted, namely Bonavera et al. (2021), Planck Collaboration (2020) and approximate Gaussian contours from DESI BAO in the $\omega_0$CDM model (DESI Collaboration, 2025a).