The Atacama Cosmology Telescope: map-based noise simulations for DR6

Zachary Atkins, Adriaan J. Duivenvoorden, William R. Coulton, Frank J. Qu, Simone Aiola, Erminia Calabrese, Grace E. Chesmore, Steve K. Choi, Mark J. Devlin, Jo Dunkley, Carlos Hervías-Caimapo, Yilun Guan, Adrien La Posta, Zack Li, Thibaut Louis, Mathew S. Madhavacheril, Kavilan Moodley, Sigurd Naess, Federico Nati, Michael D. NiemackLyman Page, Roberto Puddu, Maria Salatino, Cristóbal Sifón, Suzanne T. Staggs, Cristian Vargas, Eve M. Vavagiakis, Edward J. Wollack

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


The increasing statistical power of cosmic microwave background (CMB) datasets requires a commensurate effort in understanding their noise properties. The noise in maps from ground-based instruments is dominated by large-scale correlations, which poses a modeling challenge. This paper develops novel models of the complex noise covariance structure in the Atacama Cosmology Telescope Data Release 6 (ACT DR6) maps. We first enumerate the noise properties that arise from the combination of the atmosphere and the ACT scan strategy. We then prescribe a class of Gaussian, map-based noise models, including a new wavelet-based approach that uses directional wavelet kernels for modeling correlated instrumental noise. The models are empirical, whose only inputs are a small number of independent realizations of the same region of sky. We evaluate the performance of these models against the ACT DR6 data by drawing ensembles of noise realizations. Applying these simulations to the ACT DR6 power spectrum pipeline reveals a ∼ 20% excess in the covariance matrix diagonal when compared to an analytic expression that assumes noise properties are uniquely described by their power spectrum. Along with our public code, mnms, this work establishes a necessary element in the science pipelines of both ACT DR6 and future ground-based CMB experiments such as the Simons Observatory (SO).

Original languageEnglish (US)
Article number073
JournalJournal of Cosmology and Astroparticle Physics
Issue number11
StatePublished - Nov 1 2023

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics


  • CMBR experiments
  • Statistical sampling techniques


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