Explaining JWST Counts with Galaxy Formation Models
Manzoni G. Broadhurst T. Lim J. Liu T. Smoot G. Baugh C.M. Tompkins S. Windhorst R. Driver S. Carleton T. Frye B. Fung L. Zhang J. Cohen S.H. Conselice C.J. Grogin N.A. Jansen R.A. Koekemoer A.M. Ortiz R., III Pirzkal N. Willmer C.N.A.
1 August 2025Institute of Physics
Astrophysical Journal
2025#988Issue 2
A distinct power-law break is apparent at mAB ∼ 21 in the deep near-infrared PEARLS-JWST galaxy counts. The break becomes more pronounced at longer wavelengths, with the slope flattening smoothly with apparent magnitude in the shortest band used at 0.9 μm, and trending toward an increasingly broken slope by the longest wavelength passband of JWST’s Near Infrared Camera, 4.4 μm. This behaviour is remarkably well predicted by the GALFORM semi-analytical model of galaxy formation. We use the model to diagnose the origin of this behaviour. The features that are responsible for the break are (1) the inherent break in the luminosity function (LF); (2) the change in the volume element with redshift; (3) the redshift-dependent nature of the k-correction (with 1 contributing to the existence of the break and 2-3 contributing to its shape). We study the contribution to these effects by their morphology using the bulge-to-total stellar mass ratio. The way in which bulge-dominated galaxies populate the bright end of the LF while disk-dominated galaxies dominate the faint end is preserved in the galaxy number counts, with a characteristic stellar mass at a break of ∼1010M⊙. The shape of the number counts is mainly driven by galaxies with relatively low redshift (z ≲ 2) for a limit of mAB ≲ 28. We give a comprehensive description of why the galaxy number counts in the near-infrared PEARLS-JWST observation look the way they do and which population of galaxies is dominant at each apparent magnitude.
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Jockey Club Institute for Advanced Study, The Hong Kong University of Science and Technology, China
Department of Theoretical Physics, University of the Basque Country UPV-EHU, Bilbao, E-48040, Spain
Donostia International Physics Center (DIPC), The Basque Country, Donostia, 20018, Spain
IKERBASQUE, Basque Foundation for Science, Alameda Urquijo, 36-5, Bilbao, E-48008, Spain
Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong
Department of Physics, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong
DIPC, Basque Country UPV/EHU, San Sebastian, E-48080, Spain
Energetic Cosmos Laboratory, Nazarbayev University, Nursultan, Kazakhstan
Physics Department, University of California at Berkeley, Berkeley, 94720, CA, United States
Paris Centre for Cosmological Physics, APC, AstroParticule et Cosmologie, Université de Paris, CNRS, IN2P3, CEA/lrfu, Université Sorbonne Paris Cité, 10, rue Alice Domon et Leonie Duquet, Paris, 75205 CEDEX 13, France
Institute for Computational Cosmology (ICC), Department of Physics, Durham University, South Road, Durham, DH1 3LE, United Kingdom
International Centre for Radio Astronomy Research (ICRAR), International Space Centre (ISC), The University of Western Australia, M468, 35 Stirling Highway, Crawley, 6009, WA, Australia
School of Earth and Space Exploration, Arizona State University, Tempe, 85287-1404, AZ, United States
Department of Astronomy, Steward Observatory, University of Arizona, 933 N Cherry Ave, Tucson, 85721-0009, AZ, United States
Centre for Extragalactic Astronomy, Department of Physics, Durham University, South Road, Durham, DH1 3LE, United Kingdom
Jodrell Bank Centre for Astrophysics, University of Manchester, Alan Turing Building, Oxford Road, Manchester, M13 9PL, United Kingdom
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, 21218, MD, United States
Steward Observatory, University of Arizona, 933 N Cherry Ave, Tucson, 85721-0009, AZ, United States
Jockey Club Institute for Advanced Study
Department of Theoretical Physics
Donostia International Physics Center (DIPC)
IKERBASQUE
Department of Physics
Department of Physics
DIPC
Energetic Cosmos Laboratory
Physics Department
Paris Centre for Cosmological Physics
Institute for Computational Cosmology (ICC)
International Centre for Radio Astronomy Research (ICRAR)
School of Earth and Space Exploration
Department of Astronomy
Centre for Extragalactic Astronomy
Jodrell Bank Centre for Astrophysics
Space Telescope Science Institute
Steward Observatory
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