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    Dark Energy Survey year 6 results: Magnification modeling and its impact on galaxy clustering and galaxy-galaxy lensing cosmology

    E. Legnani1,*, J. Elvin-Poole2, D. Anbajagane3, D. Sanchez Cid4,5, A. Ferté6, N. Weaverdyck7,8, A. Porredon4,9, S. Avila4, R. Miquel10,1 et al. (DES Collaboration)

    R. Miquel10,1, J. De Vicente4, J. Coloma11, S. Samuroff12,1, W. d’Assignies1, A. Alarcon11, C. Sánchez13,1, J. Muir14,15, J. Prat16,17, N. MacCrann18, D. Bacon19, M. A. Troxel20, C. Chang16,3, M. Crocce21,11, M. R. Becker22, J. Blazek12, M. Yamamoto23,20, T. Schutt24,25,6, M. Rodriguez-Monroy26,27, G. Giannini11,3, B. Yin20, A. Amon23, K. Bechtol28, I. Sevilla-Noarbe4, T. M. C. Abbott29, M. Aguena30,31, S. Allam32, O. Alves33, F. Andrade-Oliveira5, G. M. Bernstein34, S. Bocquet35, D. Brooks36, R. Camilleri37, A. Carnero Rosell38,31,39, J. Carretero1, L. N. da Costa31, M. E. da Silva Pereira40, T. M. Davis37, S. Desai41, S. Dodelson16,32,3, P. Doel36, C. Doux34,42, J. García-Bellido43, D. Gruen35, G. Gutierrez32, S. R. Hinton37, D. L. Hollowood44, K. Honscheid45,46, D. Huterer33, D. J. James47, K. Kuehn48,49, O. Lahav36, S. Lee50,51, J. L. Marshall52, J. Mena-Fernández42, F. Menanteau53,54, J. J. Mohr35, J. Myles23, R. L. C. Ogando55,56, M. Paterno32, A. A. Plazas Malagón25,6, R. Rosenfeld57,31, E. Sanchez4, M. Smith58, M. Soares-Santos5, E. Suchyta59, and V. Vikram34 (DES Collaboration)

    • 1Institut de Física d’Altes Energies (IFAE), The Barcelona Institute of Science and Technology, Campus UAB, 08193 Bellaterra (Barcelona) Spain
    • 2Department of Physics and Astronomy, University of Waterloo, 200 University Avenue West, Waterloo, Ontario N2L 3G1, Canada
    • 3Kavli Institute for Cosmological Physics, University of Chicago, Chicago, Illinois 60637, USA
    • 4Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), Madrid, Spain
    • 5Physik-Institut, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
    • 6SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
    • 7Berkeley Center for Cosmological Physics, Department of Physics, University of California, Berkeley, California 94720, USA
    • 8Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, USA
    • 9Ruhr University Bochum, Faculty of Physics and Astronomy, Astronomical Institute, German Centre for Cosmological Lensing, 44780 Bochum, Germany
    • 10Institució Catalana de Recerca i Estudis Avançats, E-08010 Barcelona, Spain
    • 11Institute of Space Sciences (ICE, CSIC), Campus UAB, Carrer de Can Magrans, s/n, 08193 Barcelona, Spain
    • 12Department of Physics, Northeastern University, Boston, Massachusetts 02115, USA
    • 13Departament de Física, Universitat Autònoma de Barcelona (UAB), 08193 Bellaterra, Barcelona, Spain
    • 14Department of Physics, University of Cincinnati, Cincinnati, Ohio 45221, USA
    • 15Perimeter Institute for Theoretical Physics, 31 Caroline Street North, Waterloo, Ontario N2L 2Y5, Canada
    • 16Department of Astronomy and Astrophysics, University of Chicago, Chicago, Illinois 60637, USA
    • 17Nordita, KTH Royal Institute of Technology and Stockholm University, Hannes Alfvéns väg 12, SE-10691 Stockholm, Sweden
    • 18Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge, England CB3 0WA, United Kingdom
    • 19Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth, England PO1 3FX, United Kingdom
    • 20Department of Physics, Duke University Durham, North Carolina 27708, USA
    • 21Institut d’Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain
    • 22Argonne National Laboratory, 9700 South Cass Avenue, Lemont, Illinois 60439, USA
    • 23Department of Astrophysical Sciences, Princeton University, Peyton Hall, Princeton, New Jersey 08544, USA
    • 24Department of Physics, Stanford University, 382 Via Pueblo Mall, Stanford, California 94305, USA
    • 25Kavli Institute for Particle Astrophysics and Cosmology, P.O. Box 2450, Stanford University, Stanford, California 94305, USA
    • 26Instituto de Física Teórica UAM/CSIC, Universidad Autónoma de Madrid, 28049 Madrid, Spain
    • 27Laboratoire de physique des 2 infinis Irène Joliot-Curie, Bât. 100, 15 rue Georges Clémenceau, 91405 Orsay, France
    • 28Physics Department, 2320 Chamberlin Hall, University of Wisconsin-Madison, 1150 University Avenue Madison, Wisconsin 53706-1390, USA
    • 29Cerro Tololo Inter-American Observatory, NSF’s National Optical-Infrared Astronomy Research Laboratory, Casilla 603, La Serena, Chile
    • 30INAF-Osservatorio Astronomico di Trieste, via G. B. Tiepolo 11, I-34143 Trieste, Italy
    • 31Laboratório Interinstitucional de e-Astronomia-LIneA, Avenida Pastor Martin Luther King Jr, 126 Del Castilho, Nova América Offices, Torre 3000/sala 817 CEP: 20765-000, Brazil
    • 32Fermi National Accelerator Laboratory, P.O. Box 500, Batavia, Illinois 60510, USA
    • 33Department of Physics, University of Michigan, Ann Arbor, Michigan 48109, USA
    • 34Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
    • 35University Observatory, LMU Faculty of Physics, Scheinerstraße 1, 81679 Munich, Germany
    • 36Department of Physics and Astronomy, University College London, Gower Street, London, England WC1E 6BT, United Kingdom
    • 37School of Mathematics and Physics, University of Queensland, Brisbane, QLD 4072, Australia
    • 38Instituto de Astrofisica de Canarias, E-38205 La Laguna, Tenerife, Spain
    • 39Universidad de La Laguna, Dpto. Astrofísica, E-38206 La Laguna, Tenerife, Spain
    • 40Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
    • 41Department of Physics, IIT Hyderabad, Kandi, Telangana 502285, India
    • 42Université Grenoble Alpes, CNRS, LPSC-IN2P3, 38000 Grenoble, France
    • 43Instituto de Fisica Teorica UAM/CSIC, Universidad Autonoma de Madrid, 28049 Madrid, Spain
    • 44Santa Cruz Institute for Particle Physics, Santa Cruz, California 95064, USA
    • 45Center for Cosmology and Astro-Particle Physics, The Ohio State University, Columbus, Ohio 43210, USA
    • 46Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
    • 47Center for Astrophysics | Harvard and Smithsonian, 60 Garden Street, Cambridge, Massachusetts 02138, USA
    • 48Australian Astronomical Optics, Macquarie University, North Ryde, New South Wales 2113, Australia
    • 49Lowell Observatory, 1400 Mars Hill Road, Flagstaff, Arizona 86001, USA
    • 50Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California 91109, USA
    • 51Department of Physics and Astronomy, Ohio University, Clippinger Labs, Athens, Ohio 45701, USA
    • 52George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, and Department of Physics and Astronomy, Texas A and M University, College Station, Texas 77843, USA
    • 53Center for Astrophysical Surveys, National Center for Supercomputing Applications, 1205 West Clark Street, Urbana, Illinois 61801, USA
    • 54Department of Astronomy, University of Illinois at Urbana-Champaign, 1002 West Green Street, Urbana, Illinois 61801, USA
    • 55Centro de Tecnologia da Informação Renato Archer, Campinas, São Paulo, Brazil-13069-901
    • 56Observatório Nacional, Rua Gal. José Cristino 77, Rio de Janeiro, Rio de Janeiro-20921-400, Brazil
    • 57ICTP South American Institute for Fundamental Research Instituto de Física Teórica, Universidade Estadual Paulista, São Paulo, Brazil
    • 58Physics Department, Lancaster University, Lancaster, England LA1 4YB, United Kingdom
    • 59Computer Science and Mathematics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA

    • *Contact author: elegnani@ifae.es

    Phys. Rev. D 113, 123520 – Published 11 June, 2026

    DOI: https://doi.org/10.1103/rpdb-7zyn

    Abstract

    Gravitational lensing magnification alters the observed spatial distribution of galaxies and must be accounted for to prevent biases in cosmological probes of the large-scale structure. We investigate its effects on the Dark Energy Survey year 6 galaxy clustering and galaxy-galaxy lensing analyses using the fiducial lens (position tracer) sample maglim++. The combination of these two probes is referred to as the 2×2pt analysis, while the full 3×2pt analysis additionally includes cosmic shear. Magnification bias is parametrized by a coefficient that describes the response of the number of selected objects per unlensed area element to a change in the lensing convergence. We quantify this coefficient using the balrog synthetic source injection catalog to account for the complexity of the selection function and compare these results with simplified estimates. The resulting values of the magnification coefficients for each redshift bin are [3.16±0.08,2.76±0.21,4.09±0.15,4.42±0.16,4.90±0.29,4.83±0.25]. Relative to year 3, this analysis provides more precise and accurate magnification bias estimates through a larger balrog area and reweighting to better match the data properties. The cosmological results are robust when tested against various magnification parameter prior choices and also when adding cross-clustering between lens redshift bins. Neglecting magnification, however, introduces significant systematic shifts: relative to the fiducial analysis with Gaussian priors centered on the balrog-derived estimates, we observe shifts of 1.37σ in S8 and −0.84σ in Ωm when fitting 2×2pt (which are reduced to −0.61σ in S8 and −0.71σ in Ωm for 3×2pt). This agrees with findings from simulated data, demonstrating that magnification must be modeled to avoid biases. Freeing the magnification bias in lens bin 2 leads to unphysical negative values, further justifying its exclusion from the fiducial year 6 analysis.

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