Sizing the Universe with DESI Galaxy Sizes: Plain Fundamentals of Fundamental-Plane Lensing

@misc{xu2026sizing,
  title = {{Sizing the Universe with DESI Galaxy Sizes: Plain Fundamentals of Fundamental-Plane Lensing}},
  author = {Kun Xu and Jiaqi Wang and Ravi K Sheth and J Aguilar and S Ahlen and F Beutler and D Bianchi and D Brooks and A Carnero Rosell and T Claybaugh and A de la Macorra and P Doel and J.E Forero-Romero and E Gaztañaga and G Gutierrez and K Honscheid and C Howlett and M Ishak and J Jimenez and S Juneau and R Kehoe and D Kirkby and O Lahav and M Landriau and L Le Guillou and M Manera and A Meisner and R Miquel and J Moustakas and S Nadathur and J.A Newman and W.J Percival and F Prada and I Pérez-Ràfols and C Ravoux and G Rossi and R Ruggeri and E Sanchez and C Saulder and D Schlegel and M Schubnell and H Seo and J Silber and M Siudek and G Tarlé and B.A Weaver and H Zou},
  howpublished = {HAL},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.09151},
  eprint = {2609.09151},
  archivePrefix = {arXiv},
  url = {https://hal.science/hal-05758207v1},
  note = {CC BY 4.0},
}

TY  - UNPB
TI  - Sizing the Universe with DESI Galaxy Sizes: Plain Fundamentals of Fundamental-Plane Lensing
AU  - Kun Xu
AU  - Jiaqi Wang
AU  - Ravi K Sheth
AU  - J Aguilar
AU  - S Ahlen
AU  - F Beutler
AU  - D Bianchi
AU  - D Brooks
AU  - A Carnero Rosell
AU  - T Claybaugh
AU  - A de la Macorra
AU  - P Doel
AU  - J.E Forero-Romero
AU  - E Gaztañaga
AU  - G Gutierrez
AU  - K Honscheid
AU  - C Howlett
AU  - M Ishak
AU  - J Jimenez
AU  - S Juneau
AU  - R Kehoe
AU  - D Kirkby
AU  - O Lahav
AU  - M Landriau
AU  - L Le Guillou
AU  - M Manera
AU  - A Meisner
AU  - R Miquel
AU  - J Moustakas
AU  - S Nadathur
AU  - J.A Newman
AU  - W.J Percival
AU  - F Prada
AU  - I Pérez-Ràfols
AU  - C Ravoux
AU  - G Rossi
AU  - R Ruggeri
AU  - E Sanchez
AU  - C Saulder
AU  - D Schlegel
AU  - M Schubnell
AU  - H Seo
AU  - J Silber
AU  - M Siudek
AU  - G Tarlé
AU  - B.A Weaver
AU  - H Zou
PY  - 2026
DA  - 2026/09/08
PB  - HAL
DO  - 10.48550/arxiv.2609.09151
UR  - https://hal.science/hal-05758207v1
AB  - 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≡Δlog_10R_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_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_e with I_e inevitably induces a magnitude dependence in δ̅_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 ≃ −0.2 times the size bias. FP lensing therefore provides a clean, spectroscopic and complementary probe of cosmic structure.
ER  -