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Dr John Helly's Outputs (35)

The unabridged satellite luminosity function of Milky Way-like galaxies in ΛCDM: the contribution of ‘orphan’ satellites (2025)
Journal Article
Santos-Santos, I. M. E., Frenk, C. S., Navarro, J. F., Cole, S., & Helly, J. (2025). The unabridged satellite luminosity function of Milky Way-like galaxies in ΛCDM: the contribution of ‘orphan’ satellites. Monthly Notices of the Royal Astronomical Society, 540(1), 1107-1123. https://doi.org/10.1093/mnras/staf749

We study the abundance, radial distribution, and orbits of luminous satellites in simulations of Milky Way-mass dark haloes in the cold dark matter (ΛCDM) cosmology. We follow the evolution of a halo from the Aquarius project and the formation of its... Read More about The unabridged satellite luminosity function of Milky Way-like galaxies in ΛCDM: the contribution of ‘orphan’ satellites.

FLAMINGO: combining kinetic SZ effect and galaxy–galaxy lensing measurements to gauge the impact of feedback on large-scale structure (2025)
Journal Article
McCarthy, I. G., Amon, A., Schaye, J., Schaan, E., Angulo, R. E., Salcido, J., Schaller, M., Bigwood, L., Elbers, W., Kugel, R., Helly, J. C., Forouhar Moreno, V. J., Frenk, C. S., McGibbon, R. J., Ondaro-Mallea, L., & van Daalen, M. P. (2025). FLAMINGO: combining kinetic SZ effect and galaxy–galaxy lensing measurements to gauge the impact of feedback on large-scale structure. Monthly Notices of the Royal Astronomical Society, 540(1), 143-163. https://doi.org/10.1093/mnras/staf731

Energetic feedback processes associated with accreting supermassive black holes can expel gas from massive haloes and significantly alter various measures of clustering on Mpc scales, potentially biasing the values of cosmological parameters inferred... Read More about FLAMINGO: combining kinetic SZ effect and galaxy–galaxy lensing measurements to gauge the impact of feedback on large-scale structure.

On the accuracy of dark matter halo merger trees and the consequences for semi-analytic models of galaxy formation (2025)
Journal Article
Chandro-Gómez, Á., Lagos, C. D. P., Power, C., Moreno, V. J. F., Helly, J. C., Lacey, C. G., McGibbon, R. J., Schaller, M., & Schaye, J. (2025). On the accuracy of dark matter halo merger trees and the consequences for semi-analytic models of galaxy formation. Monthly Notices of the Royal Astronomical Society, 539(2), 776-807. https://doi.org/10.1093/mnras/staf519

Galaxy formation and evolution models, such as semi-analytic models, are powerful theoretical tools for predicting how galaxies evolve across cosmic time. These models follow the evolution of galaxies based on the halo assembly histories inferred fro... Read More about On the accuracy of dark matter halo merger trees and the consequences for semi-analytic models of galaxy formation.

The emperor’s new arc: gigaparsec patterns abound in a ΛCDM universe (2025)
Journal Article
Sawala, T., Teeriaho, M., Frenk, C. S., Helly, J., Jenkins, A., Racz, G., Schaller, M., & Schaye, J. (2025). The emperor’s new arc: gigaparsec patterns abound in a ΛCDM universe. Monthly Notices of the Royal Astronomical Society: Letters, 541(1), L22-L27. https://doi.org/10.1093/mnrasl/slaf021

Recent discoveries of apparent large-scale features in the structure of the Universe extending over many hundreds of megaparsecs, have been claimed to contradict the large-scale isotropy and homogeneity foundational to the standard (Lambda cold dark... Read More about The emperor’s new arc: gigaparsec patterns abound in a ΛCDM universe.

The FLAMINGO project: the coupling between baryonic feedback and cosmology in light of the S8 tension (2025)
Journal Article
Elbers, W., Frenk, C. S., Jenkins, A., Li, B., Helly, J. C., Kugel, R., Schaller, M., Schaye, J., Braspenning, J., Kwan, J., McCarthy, I. G., Salcido, J., van Daalen, M. P., Vandenbroucke, B., & Pascoli, S. (2025). The FLAMINGO project: the coupling between baryonic feedback and cosmology in light of the S8 tension. Monthly Notices of the Royal Astronomical Society, 537(2), 2160-2178. https://doi.org/10.1093/mnras/staf093

Large-scale structure surveys have reported measurements of the density of matter, Ωm, and the amplitude of clustering, σ8, that are in tension with the values inferred from observations of the cosmic microwave background. While this may be a sign of... Read More about The FLAMINGO project: the coupling between baryonic feedback and cosmology in light of the S8 tension.

EIGER. VI. The Correlation Function, Host Halo Mass, and Duty Cycle of Luminous Quasars at z ≳ 6 (2024)
Journal Article
Eilers, A.-C., Mackenzie, R., Pizzati, E., Matthee, J., Hennawi, J. F., Zhang, H., Bordoloi, R., Kashino, D., Lilly, S. J., Naidu, R. P., Simcoe, R. A., Yue, M., Frenk, C. S., Helly, J. C., Schaller, M., & Schaye, J. (2024). EIGER. VI. The Correlation Function, Host Halo Mass, and Duty Cycle of Luminous Quasars at z ≳ 6. The Astrophysical Journal, 974(2), Article 275. https://doi.org/10.3847/1538-4357/ad778b

We expect luminous (M 1450 ≲ −26.5) high-redshift quasars to trace the highest-density peaks in the early Universe. Here, we present observations of four z ≳ 6 quasar fields using JWST/NIRCam in the imaging and wide-field slitless spectroscopy mode a... Read More about EIGER. VI. The Correlation Function, Host Halo Mass, and Duty Cycle of Luminous Quasars at z ≳ 6.

The FLAMINGO project: a comparison of galaxy cluster samples selected on mass, X-ray luminosity, Compton-Y parameter, or galaxy richness (2024)
Journal Article
Kugel, R., Schaye, J., Schaller, M., McCarthy, I. G., Braspenning, J., Helly, J. C., Forouhar Moreno, V. J., & McGibbon, R. J. (2024). The FLAMINGO project: a comparison of galaxy cluster samples selected on mass, X-ray luminosity, Compton-Y parameter, or galaxy richness. Monthly Notices of the Royal Astronomical Society, 534(3), 2378-2396. https://doi.org/10.1093/mnras/stae2218

Swift: A modern highly-parallel gravity and smoothed particle hydrodynamics solver for astrophysical and cosmological applications (2024)
Journal Article
Schaller, M., Borrow, J., Draper, P. W., Ivkovic, M., McAlpine, S., Vandenbroucke, B., Bahé, Y., Chaikin, E., Chalk, A. B. G., Chan, T. K., Correa, C., van Daalen, M., Elbers, W., Gonnet, P., Hausammann, L., Helly, J., Huško, F., Kegerreis, J. A., Nobels, F. S. J., Ploeckinger, S., …Xiang, Z. (2024). Swift: A modern highly-parallel gravity and smoothed particle hydrodynamics solver for astrophysical and cosmological applications. Monthly Notices of the Royal Astronomical Society, 530(2), 2378–2419. https://doi.org/10.1093/mnras/stae922

Numerical simulations have become one of the key tools used by theorists in all the fields of astrophysics and cosmology. The development of modern tools that target the largest existing computing systems and exploit state-of-the-art numerical method... Read More about Swift: A modern highly-parallel gravity and smoothed particle hydrodynamics solver for astrophysical and cosmological applications.

Non-linear CMB lensing with neutrinos and baryons: FLAMINGO simulations versus fast approximations (2024)
Journal Article
Upadhye, A., Kwan, J., McCarthy, I. G., Salcido, J., Helly, J. C., Kugel, R., …Broxterman, J. C. (2024). Non-linear CMB lensing with neutrinos and baryons: FLAMINGO simulations versus fast approximations. Monthly Notices of the Royal Astronomical Society, 529(2), 1862-1876. https://doi.org/10.1093/mnras/stae663

Weak lensing of the cosmic microwave background is rapidly emerging as a powerful probe of neutrinos, dark energy, and new
physics. We present a fast computation of the non-linear CMB lensing power spectrum that combines non-linear perturbation
the... Read More about Non-linear CMB lensing with neutrinos and baryons: FLAMINGO simulations versus fast approximations.

The FLAMINGO project: baryonic impact on weak gravitational lensing convergence peak counts (2024)
Journal Article
Broxterman, J. C., Schaller, M., Schaye, J., Hoekstra, H., Kuijken, K., Helly, J. C., Kugel, R., Braspenning, J., Elbers, W., Frenk, C. S., Kwan, J., McCarthy, I. G., Salcido, J., van Daalen, M. P., & Vandenbroucke, B. (2024). The FLAMINGO project: baryonic impact on weak gravitational lensing convergence peak counts. Monthly Notices of the Royal Astronomical Society, 529(3), 2309-2326. https://doi.org/10.1093/mnras/stae698

Weak gravitational lensing convergence peaks, the local maxima in weak lensing convergence maps, have been shown to contain valuable cosmological information complementary to commonly used two-point statistics. To exploit the full power of weak lensi... Read More about The FLAMINGO project: baryonic impact on weak gravitational lensing convergence peak counts.

The FLAMINGO project: revisiting the S8 tension and the role of baryonic physics (2023)
Journal Article
Elbers, W., Helly, J., Frenk, C., McCarthy, I. G., Salcido, J., Schaye, J., …Upadhye, A. (2023). The FLAMINGO project: revisiting the S8 tension and the role of baryonic physics. Monthly Notices of the Royal Astronomical Society, 526(4), 5494–5519. https://doi.org/10.1093/mnras/stad3107

A number of recent studies have found evidence for a tension between observations of large-scale structure (LSS) and the predictions of the standard model of cosmology with the cosmological parameters fit to the cosmic microwave background (CMB). The... Read More about The FLAMINGO project: revisiting the S8 tension and the role of baryonic physics.

The FLAMINGO project: cosmological hydrodynamical simulations for large-scale structure and galaxy cluster surveys (2023)
Journal Article
Schaye, J., Kugel, R., Schaller, M., Helly, . J. C., Braspenning, J., Elbers, W., …Nobels, F. S. J. (2023). The FLAMINGO project: cosmological hydrodynamical simulations for large-scale structure and galaxy cluster surveys. Monthly Notices of the Royal Astronomical Society, 526(4), 4978–5020. https://doi.org/10.1093/mnras/stad2419

We introduce the Virgo Consortium’s FLAMINGO suite of hydrodynamical simulations for cosmology and galaxy cluster physics. To ensure the simulations are sufficiently realistic for studies of large-scale structure, the subgrid prescriptions for stella... Read More about The FLAMINGO project: cosmological hydrodynamical simulations for large-scale structure and galaxy cluster surveys.

The Milky Way’s plane of satellites is consistent with ΛCDM (2022)
Journal Article
Sawala, T., Cautun, M., Frenk, C., Helly, J., Jasche, J., Jenkins, A., Johansson, P. H., Lavaux, G., McAlpine, S., & Schaller, M. (2023). The Milky Way’s plane of satellites is consistent with ΛCDM. Nature Astronomy, 7(4), 481-491. https://doi.org/10.1038/s41550-022-01856-z

The Milky Way is surrounded by 11 ‘classical’ satellite galaxies in a remarkable configuration: a thin plane that is possibly rotationally supported. Such a structure is thought to be highly unlikely to arise in the standard (ΛCDM) cosmological model... Read More about The Milky Way’s plane of satellites is consistent with ΛCDM.

Is the Core-cusp Problem a Matter of Perspective? Jeans Anisotropic Modeling against Numerical Simulations (2022)
Journal Article
Wang, W., Zhu, L., Li, Z., Chen, Y., Han, J., He, F., …Gomez, F. A. (2022). Is the Core-cusp Problem a Matter of Perspective? Jeans Anisotropic Modeling against Numerical Simulations. Astrophysical Journal, 941(2), Article 108. https://doi.org/10.3847/1538-4357/ac9b19

Mock member stars for 28 dwarf galaxies are constructed from the cosmological auriga simulation, which reflects the dynamical status of realistic stellar tracers. Axisymmetric Jeans Anisotropic Multi-Gaussian Expansion (jam) modeling is applied to 60... Read More about Is the Core-cusp Problem a Matter of Perspective? Jeans Anisotropic Modeling against Numerical Simulations.

The DESI N-body simulation project – I. Testing the robustness of simulations for the DESI dark time survey (2022)
Journal Article
Grove, C., Chuang, C.-H., Devi, N. C., Garrison, L., L’Huillier, B., Feng, Y., Helly, J., Hernández-Aguayo, C., Alam, S., Zhang, H., Yu, Y., Cole, S., Eisenstein, D., Norberg, P., Wechsler, R., Brooks, D., Dawson, K., Landriau, M., Meisner, A., Poppett, C., …Valenzuela, O. (2022). The DESI N-body simulation project – I. Testing the robustness of simulations for the DESI dark time survey. Monthly Notices of the Royal Astronomical Society, 515(2), https://doi.org/10.1093/mnras/stac1947

Analysis of large galaxy surveys requires confidence in the robustness of numerical simulation methods. The simulations are used to construct mock galaxy catalogues to validate data analysis pipelines and identify potential systematics. We compare th... Read More about The DESI N-body simulation project – I. Testing the robustness of simulations for the DESI dark time survey.

SIBELIUS-DARK: a galaxy catalogue of the local volume from a constrained realization simulation (2022)
Journal Article
McAlpine, S., Helly, J. C., Schaller, M., Sawala, T., Lavaux, G., Jasche, J., Frenk, C. S., Jenkins, A., Lucey, J. R., & Johansson, P. H. (2022). SIBELIUS-DARK: a galaxy catalogue of the local volume from a constrained realization simulation. Monthly Notices of the Royal Astronomical Society, 512(4), 5823-5847. https://doi.org/10.1093/mnras/stac295

We present SIBELIUS-DARK, a constrained realization simulation of the local volume to a distance of 200 Mpc from the Milky Way. SIBELIUS-DARK is the first study of the ‘Simulations Beyond The Local Universe’ (SIBELIUS) project, which has the goal of... Read More about SIBELIUS-DARK: a galaxy catalogue of the local volume from a constrained realization simulation.

Halo merger tree comparison: impact on galaxy formation models (2021)
Journal Article
Gómez, J. S., Padilla, N., Helly, J., Lacey, C., Baugh, C., & Lagos, C. (2022). Halo merger tree comparison: impact on galaxy formation models. Monthly Notices of the Royal Astronomical Society, 510(4), 5500-5519. https://doi.org/10.1093/mnras/stab3661

We examine the effect of using different halo finders and merger tree building algorithms on galaxy properties predicted using the GALFORM semi-analytical model run on a high resolution, large volume dark matter simulation. The halo finders/tree buil... Read More about Halo merger tree comparison: impact on galaxy formation models.