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Cosmology

Members of the CCSE Cosmology Team

  • Mahesh Natarajan
  • Jean Sexton


    • Nyx: an adaptive mesh, N-body compressible cosmological hydrodynamics simulation code

    Cosmological simulation

    Nyx is hosted at http://www.github.com/AMReX-Astro/Nyx

    with more information about Nyx at

    http://AMReX-Astro.github.io/Nyx

    The gif shows the temporal evolution of gas density in a cosmological simulation showing high-density regions, such as galaxy clusters, filaments, and cosmic structures formed by the gravitational collapse of baryonic matter (gas) and dark matter.

    The scientific output from cosmology experiments like DESI, the Simons Observatory, CMB-S4, and the Vera Rubin Observatory are increasingly limited not by statistical power, but by our ability to understand and control systematic uncertainties. This can only be achieved through advanced numerical simulations. Simulating the Universe at the scale of volumes representative of modern surveys, while at the same time accurately modeling physics with the spatio-temporal resolution required to interpret the observational data is a daunting task. Researchers from the CCSE and the Computational Cosmology Center are taking on this challenge by developing state-of-the-art computational methods, and implementing them in the Nyx code.

    There are two major research directions Nyx team is taking on:

    • modeling the Lyman alpha forest and
    • building the next generation mock skies.

    The first, funded under the HEP-ASCR SciDAC-5 program, aims to model the Lyman-alpha forest and directly supports DESI by providing theoretical models for the behavior of gas in the intergalactic medium, which produces the Lyman-alpha forest signal. The second project, funded by LBNL's LDRD, combines simulations with AI methods to generate mock lightcones with observables relevant to future cosmic microwave background (CMB) and optical galaxy surveys, such as those conducted by the Vera Rubin Observatory.

    A description of the image
    Fig. 1: The isocontours of flux (fraction of light transmitted through the interglactic medium) in the Lyman α simulation, which is indicative of the distribution of neutral Hydrogen.
    Images Side by Side
    A description of the image
    Fig. 2: Partial-sky lightcone showing dark matter particles in a solid angle of 0.84 steradians from red shift z = 0 to z = 4.5 (obtained from a simulation with 453 million dark matter particles)
    A description of the image
    Fig. 3: A HEALPix image showing the full-sky convergence κ due to weak gravitational lensing in a dark matter simulation with 453 million particles. This physically represents the dimensionless surface mass density of the dark matter particles along the line of sight.

    Publications

    Solene Chabanier, J.D. Emberson, Zarija Lukic, Jesus Pulido, Salman Habib, Esteban Rangel, Jean Sexton, Nicholas Frontiere, Michael Buehlmann, Modeling the Lyman-alpha forest with Eulerian and SPH hydrodynamical methods, MNRAS, 518, 3, January 2023. [arxiv] [doi]

    Jean Sexton, Zarija Lukic, Ann Almgren, Chris Daley, Brian Friesen, Andrew Myers, and Weiqun Zhang, Nyx: A Massively Parallel AMR Code for Computational Cosmology, Journal of Open Source Software, 6(63), 3068, 2021. [doi]

    Brian Friesen, Ann Almgren, Zarija Lukic, Gunther Weber, Dmitriy Morozov, Vincent Beckner, Marcus Day, "In situ and in-transit analysis of cosmological simulations," Computational Astrophysics and Cosmology, 3:4, 2016 [pdf]

    Zarija Lukic, Casey Stark, Peter Nugent, Martin White, Avery Meiksin, Ann Almgren, "The Lyman-alpha forest in optically-thin hydrodynamical simulations," Monthly Notices of the Royal Astronomical Society, 446, 3697-3724, 2015. [arxiv].

    A. S. Almgren, J. B. Bell, M.J. Lijewski, Z. Lukic, E. Van Andel, "Nyx: A Massively Parallel AMR Code for Computational Cosmology" Astrophysical Journal, 765, 39, 2013. [pdf]