Sizing the Universe with DESI Galaxy Sizes: Plain Fundamentals of Fundamental-Plane Lensing
Year: 2026
Type: preprint
Abstract: Weak gravitational lensing provides a powerful way to map cosmic structure, but most current measurements rely on galaxy shape distortions from deep imaging surveys and are affected by systematics such as intrinsic alignments, photometric-redshift uncertainties and shape-measurement biases. Here we present a spectroscopic galaxy-galaxy lensing magnification measurement using Fundamental-Plane (FP) size residuals, $δ_r\equivΔ\log_{10}R_\mathrm{e}$, from 3.26 million DESI luminous red galaxy (LRG) sources behind DESI Bright Galaxy Survey lenses. The FP-like relation predicts the intrinsic sizes of LRGs from lensing-invariant quantities, including velocity dispersion $σ_0$ and surface brightness $I_\mathrm{e}$, with a scatter of about 0.06-0.07 dex. Lensing magnifies LRG sizes, giving the direct convergence response $δ_r(κ)=κ/\ln 10$, but we show that the full lensing response is modified by magnification bias, because fitting $R_\mathrm{e}$ with $I_\mathrm{e}$ inevitably induces a magnitude dependence in $\barδ_r(m)$. After calibrating this response, we recover surface-density profiles with uncertainties comparable to those from individual Stage-III shear surveys using 5-20 million higher-redshift sources. The corresponding excess surface-density profiles agree with shear-based measurements. We further show that the estimator is robust to size-measurement uncertainties, with a convergence multiplicative bias only $\simeq -0.2$ times the size bias. FP lensing therefore provides a clean, spectroscopic and complementary probe of cosmic structure.
Source: arXiv (Cornell University)
Authors: Xu, Kun, Wang, Jiaqi, Sheth, Ravi K., Aguilar, J., Ahlen, S., Beutler, F., Bianchi, D., Brooks, D., Rosell, A. Carnero, Claybaugh, T., de la Macorra, A., Doel, P., Forero-Romero, J. E., Gaztañaga, E., Gutierrez, G., Honscheid, K., Howlett, C., Ishak, M., Jimenez, J., Juneau, S., Kehoe, R., Kirkby, D., Lahav, O., Landriau, M., Guillou, L. Le, Manera, M., Meisner, A., Miquel, R., Moustakas, J., Nadathur, S., Newman, J. A., Percival, W. J., Prada, F., Pérez-Ràfols, I., Ravoux, C., Rossi, G., Ruggeri, R., Sanchez, E., Saulder, C., Schlegel, D., Schubnell, M., Seo, H., Silber, J., Siudek, M., Tarlé, G., Weaver, B. A., Zou, H.
Institutions: University of Pennsylvania, Shanghai Jiao Tong University, Durham University, Lawrence Berkeley National Laboratory, Boston University, Royal Observatory, University of Edinburgh, University of Milan, Brera Astronomical Observatory, University College London, Universidad de La Laguna, Instituto de Astrofísica de Canarias, Universidad Nacional Autónoma de México, Universidad de Los Andes, Fermi National Accelerator Laboratory, The University of Queensland, The University of Texas at Dallas, Institute for High Energy Physics, Barcelona Institute of Science and Technology, NSF NOIRLab, Southern Methodist University, Centre National de la Recherche Scientifique, University of California, Irvine, Sorbonne Université, Laboratoire de Physique Nucléaire et de Hautes Énergies, Institut National de Physique Nucléaire et de Physique des Particules, Universitat Autònoma de Barcelona, Institució Catalana de Recerca i Estudis Avançats, University of Portsmouth, University of Pittsburgh, Instituto de Astrofísica de Andalucía, Laboratoire de Physique de Clermont Auvergne, Sejong University, Queensland University of Technology, Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, Max Planck Institute for Extraterrestrial Physics, University of Michigan, Ohio University, Institute of Space Sciences, Chinese Academy of Sciences, National Astronomical Observatories
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7212086024