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Title: The Atacama Cosmology Telescope: DR6 power spectrum foreground model and validation

Journal Article · · Journal of Cosmology and Astroparticle Physics
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  1. Univ. Paris Cite (France); Cardiff Univ., Wales (United Kingdom)
  2. Columbia Univ., New York, NY (United States)
  3. Columbia Univ., New York, NY (United States); Flatiron Institute, New York, NY (United States)
  4. Princeton Univ., NJ (United States)
  5. Cornell Univ., Ithaca, NY (United States); Univ. Paris Cite (France)
  6. Univ. of Cambridge (United Kingdom); Kavli Institute for Cosmology Cambridge (United Kingdom)
  7. Cardiff Univ., Wales (United Kingdom)
  8. Univ. of California, Riverside, CA (United States)
  9. Stanford Univ., CA (United States). Kavli Institute for Particle Astrophysics & Cosmology
  10. Max Planck Institute for Astrophysics, Garching (Germany)
  11. California Institute of Technology (CalTech), Pasadena, CA (United States)
  12. Univ. of Toronto, ON (Canada)
  13. Arizona State Univ., Tempe, AZ (United States)
  14. Univ. of Oxford (United Kingdom)
  15. Université Paris-Saclay, Orsay (France)
  16. Univ. of KwaZulu-Natal, Durban (South Africa)
  17. Univ. of Oslo (Norway)
  18. Haverford College, PA (United States)
  19. Stanford Univ., CA (United States). Kavli Institute for Particle Astrophysics & Cosmology; SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)
  20. Stony Brook Univ., NY (United States)
  21. Pontifical Catholic Univ. of Valparaíso (Chile)
  22. Carnegie Mellon Univ., Pittsburgh, PA (United States)
  23. NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States)

We discuss the model of astrophysical emission at millimeter wavelengths used to characterize foregrounds in the multi-frequency power spectra of the Atacama Cosmology Telescope (ACT) Data Release 6 (DR6), expanding on Louis et al. (2025) (2503.14452). We detail several tests to validate the capability of the DR6 parametric foreground model to describe current observations and complex simulations, and show that cosmological parameter constraints are robust against model extensions and variations. We demonstrate consistency of the model with pre-DR6 ACT data and observations from Planck and the South Pole Telescope. We evaluate the implications of using different foreground templates and extending the model with new components and/or free parameters. In all scenarios, the DR6 ΛCDM and ΛCDM+Neff cosmological parameters shift by less than 0.5σ relative to the baseline constraints. Some foreground parameters shift more; we estimate their systematic uncertainties associated with modeling choices. From our constraint on the kinematic Sunyaev-Zel'dovich power, we obtain a conservative limit on the duration of reionization of Δzrei < 4.4, assuming a reionization midpoint consistent with optical depth measurements and a minimal low-redshift contribution, with varying assumptions for this component leading to tighter limits. Finally, we analyze realistic non-Gaussian, correlated microwave sky simulations containing Galactic and extragalactic foreground fields, built independently of the DR6 parametric foreground model. Processing these simulations through the DR6 power spectrum and likelihood pipeline, we recover the input cosmological parameters of the underlying cosmic microwave background field, a new demonstration for small-scale CMB analysis. These tests validate the robustness of the ACT DR6 foreground model and cosmological parameter constraints.

Research Organization:
State Univ. of New York (SUNY), Stony Brook, NY (United States)
Sponsoring Organization:
USDOE Office of Science (SC), High Energy Physics (HEP)
Grant/Contract Number:
SC0025309
OSTI ID:
3008496
Journal Information:
Journal of Cosmology and Astroparticle Physics, Journal Name: Journal of Cosmology and Astroparticle Physics Journal Issue: 10 Vol. 2025; ISSN 1475-7516
Publisher:
Institute of Physics (IOP)Copyright Statement
Country of Publication:
United States
Language:
English

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