PAIRS: PAIRwise velocitieS in the context of the cosmic web ve
PAIRS is a cosmology project that uses how galaxies move toward or away from each other to learn more about what the Universe is made of and how it evolves, especially on small, complex scales that current methods cannot fully exploit.
Meet the team
Cosmologist leading the project, with expertise in theoretical modelling, cosmological inference, and the physics of large-scale structure
Doctor in Astronomy and Physics by the National University of Cordoba, and specialist in numerical simulations and data analysis, responsible for handling large cosmological simulations and the study of the cosmic web in observations and simulations.
Doctoral researcher with a master in Physics by the University of Copenhagen
is working on connecting theory and simulations, and extending the current analytical templates for more realistic scenarios.
What PAIRS is about
Galaxies are not standing still: gravity makes them stream towards denser regions, and these peculiar motions carry information about dark matter, dark energy, and the overall matter content of the Universe. PAIRS focuses on pairwise velocities – the typical relative motion of pairs of galaxies – and on where those pairs live in the “cosmic web” of voids, walls, filaments and nodes. By combining this dynamical view with advanced simulations, PAIRS aims to turn galaxy motions into a powerful, independent test of our cosmological model.
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PAIRS has four main objectives:​
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Use galaxy motions to obtain robust, independent constraints on key cosmological parameters, such as the matter density, the Hubble expansion rate, and the amplitude of cosmic clustering.​
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Develop improved models of how galaxies trace dark matter that remain valid on very small, highly non-linear scales.​
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Understand how processes like galaxy and halo mergers modify the standard assumptions behind pairwise-velocity theory.​
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Quantify how the environment in the cosmic web (voids, walls, filaments, nodes) affects galaxy motions and the galaxy–halo connection.
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How we work
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To achieve these goals, PAIRS combines theory, simulations, and modern statistical tools:​
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Revisit and extend the theoretical equation that describes how pairs of galaxies fall towards each other, allowing for non-conservative effects such as mergers.​
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Use large, state-of-the-art cosmological simulations (like TNG, Quijote and Bolshoi) to measure the motions of dark matter, haloes and galaxies in controlled virtual universes.​
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Segment these simulations into cosmic-web environments using advanced topology-based algorithms, identifying voids, walls, filaments and nodes.​
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Build and test enhanced galaxy bias models by matching analytical predictions to the detailed simulation measurements across environments and scales.​
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Run dedicated Markov Chain Monte Carlo analyses to translate the new velocity-based statistics into constraints on cosmological parameters and to forecast their impact for current and future galaxy surveys.
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Scope and impact
PAIRS is structured in three stages, progressing from theoretical foundations and data preparation, through measurements and model building, to final cosmological constraints. The project will deliver new theoretical templates, carefully curated simulation catalogues, improved small-scale bias models, and publicly useful cosmological constraints and forecasts that highlight the added value of galaxy motions for understanding dark matter, dark energy and gravity on cosmic scales.
Coming soon
