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

Abstract 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+ N eff cosmological parameters shift by less than 0.5 σ 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 Δ z rei < 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.

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Publication Details

Journal
Journal of Cosmology and Astroparticle Physics
Published
2025-10-01
DOI
https://doi.org/10.1088/1475-7516/2025/10/082
Citations
2
Primary Topic
Astrophysics and Cosmic Phenomena
Type
article
Field-Weighted Citation Impact
3.74
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The Atacama Cosmology Telescope: DR6 power spectrum foreground model and validation

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Journal of Cosmology and Astroparticle Physics
Astrophysics and Cosmic Phenomena
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article

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

Sigurd Næss, Renée Hložek, Boris Bolliet, Susan E. Clark, Samuel Goldstein, Hy Trac, Kavilan Moodley, Yogesh Mehta, Hidde T. Jense, Zachary Atkins, J. Colin Hill, Brandon S. Hensley, Kristen M. Surrao, Frank J. Qu, Adriaan J. Duivenvoorden, Suzanne T. Staggs, Thibaut Louis, Neelima Sehgal, Alexander van Engelen, Steve K. Choi, Erminia Calabrese, Darby Kramer, Cristobál Sifón, S. Giardiello, Benjamin Beringue, Nicholas Battaglia, Edward J. Wollack, Adrien La Posta, Bernardita Ried Guachalla, Bruce Partridge, Jo Dunkley
article en
2 citations

Abstract

Abstract 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+ N eff cosmological parameters shift by less than 0.5 σ 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 Δ z rei < 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.

Journal of Cosmology and Astroparticle PhysicsVol. 2025(10)
Université Paris Cité (FR), Laboratoire AstroParticule et Cosmologie (FR), Laboratoire de Physique des 2 Infinis Irène Joliot-Curie (FR)
Openalex Percentile: Top 7%
Astrophysics and Cosmic Phenomena
3.74
DOIOpen Access PDFOpenAlex
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