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

Beringue, Benjamin, Surrao, Kristen M., Hill, J. Colin, Atkins, Zachary, Battaglia, Nicholas, Bolliet, Boris, Calabrese, Erminia ORCID: https://orcid.org/0000-0003-0837-0068, Choi, Steve K., Clark, Susan E., Duivenvoorden, Adriaan J., Dunkley, Jo, Giardiello, Serena, Goldstein, Samuel, Hensley, Brandon S., Hložek, Renée, Jense, Hidde T., Kramer, Darby, La Posta, Adrien, Louis, Thibaut, Mehta, Yogesh, Moodley, Kavilan, Naess, Sigurd, Partridge, Bruce, Qu, Frank J., Ried Guachalla, Bernardita, Sehgal, Neelima, Sifón, Cristóbal, Staggs, Suzanne T., Trac, Hy, Van Engelen, Alexander and Wollack, Edward J. 2025. The Atacama Cosmology Telescope: DR6 power spectrum foreground model and validation. Journal of Cosmology and Astroparticle Physics 2025 (10) , 082. 10.1088/1475-7516/2025/10/082

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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 0.5σ 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 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.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Schools > Physics and Astronomy
Additional Information:	License information from Publisher: LICENSE 1: URL: http://creativecommons.org/licenses/by/4.0/, Type: cc-by
Publisher:	IOP Publishing
Date of First Compliant Deposit:	27 October 2025
Date of Acceptance:	19 August 2025
Last Modified:	27 Oct 2025 13:47
URI:	https://orca.cardiff.ac.uk/id/eprint/181919

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