Probing Projection Effects in Optically-Selected Clusters with Velocity Dispersions Outliers
Year: 2026
Type: preprint
Abstract: The evolution of galaxy cluster abundance is a powerful probe of cosmology, but its efficacy depends on our ability to understand and control for systematics in the selection and mass estimation of clusters. We study redMaPPer-selected clusters in the Cardinal simulation, which simulates the DES Y3 observational conditions. Specifically, we investigate the line-of-sight velocity distributions of cluster member galaxies in 12,272 simulated clusters. We find that a significant fraction of clusters, 35%, have velocity dispersions that are high compared to their richness with an offset of $\sim 400$ km s$^{-1}$ between the outliers and the main population. A similar population of velocity dispersion outliers was found in the DES Y3 data. Nearly all of the outliers (98%) in a low-richness subsample have non-Gaussian velocity distributions, and they are more likely than the main population to have significant velocity substructure. These clusters also tend to have higher redshifts than clusters with typical velocity dispersions, and they show a larger scatter between halo mass and richness. Overall, our results point to a significant contamination of redMaPPer-selected samples from line of sight structure, particularly at high redshifts and low richness. Comparison to the Buzzard simulations shows similar results.
Source: arXiv (Cornell University)
Institutions: University of California, Santa Cruz, The Ohio State University, University of Pennsylvania, Southern Methodist University, SLAC National Accelerator Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Lawrence Berkeley National Laboratory, Centre National de la Recherche Scientifique, Université Paris Cité, Laboratoire AstroParticule et Cosmologie, Institut National de Physique Nucléaire et de Physique des Particules, Stanford University
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: National Science Foundation, U.S. Department of Energy, University of Pennsylvania, Ohio State University, University of Chicago, University of Portsmouth, Centres de Recerca de Catalunya, University College London, European Commission, University of Sussex, Deutsche Forschungsgemeinschaft, Generalitat de Catalunya, Ministério da Ciência, Tecnologia e Inovação, Conselho Nacional de Desenvolvimento Científico e Tecnológico, Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro, Financiadora de Estudos e Projetos, Ministerio de Ciencia e Innovación, Institut de Física d'Altes Energies, University of Illinois at Urbana-Champaign, Office of Science, Science and Technology Facilities Council, European Regional Development Fund, Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, High Energy Physics, Integrated Electronics Engineering Center, Binghamton University, Argonne National Laboratory, Fermilab, Lawrence Berkeley National Laboratory, SLAC National Accelerator Laboratory
Awards: G1054097061, G1265542407, G1313983767, G1336129044, G154696372, G1746333638, G179674260, G1907584174, G2233160401, G2401681081, G2554159582, G302750986, G3154116105, G3439265645, G3523651922, The Dark Energy Survey Data Management Operations, G3870743921, G3906089732, G4404904460, G454676879, G4655338613, G498139845, G5616713406, G585908603, G6513613686, G656518222, G6676276723, G6941735741, G716412294, G7788408655, G7835623888, G8284171658, Collaborative Research: The Dark Energy Survey Data Management Operations, G86560745, G8920660035, G946511789, G969889393
OpenAlex ID: W7212065740