AtLAST -- Determination of Halo Mass Density Profiles at kpc Scales through Magnification Bias

Magnification bias, the lensing-induced modification of background source number counts, provides a uniquely powerful probe of the mass density profiles of galaxies and clusters down to kpc scales. Unlike shear-based weak lensing, magnification bias does not rely on galaxy shapes and thus avoids dominant small-scale systematics. Existing studies, however, are limited by sky coverage, positional uncertainty, and insufficiently deep, confusion-limited submillimetre (submm) surveys. A next-generation wide-field, high-throughput submm facility like the proposed 50m-telescope AtLAST is required to unlock this technique’s full diagnostic power.