The Atacama Cosmology Telescope: Mitigating the Impact of Extragalactic Foregrounds for the DR6 Cosmic Microwave Background Lensing Analysis

Niall MacCrann, Blake D. Sherwin, Frank J. Qu, Toshiya Namikawa, Mathew S. Madhavacheril, Irene Abril-Cabezas, Rui An, Jason E. Austermann, Nicholas Battaglia, Elia S. Battistelli, James A. Beall, Boris Bolliet, J. Richard Bond, Hongbo Cai, Erminia Calabrese, William R. Coulton, Omar Darwish, Shannon M. Duff, Adriaan J. Duivenvoorden, Jo DunkleyGerrit S. Farren, Simone Ferraro, Joseph E. Golec, Yilun Guan, Dongwon Han, Carlos Hervías-Caimapo, J. Colin Hill, Matt Hilton, Renée Hložek, Johannes Hubmayr, Joshua Kim, Zack Li, Arthur Kosowsky, Thibaut Louis, Jeff McMahon, Gabriela A. Marques, Kavilan Moodley, Sigurd Naess, Michael D. Niemack, Lyman Page, Bruce Partridge, Emmanuel Schaan, Neelima Sehgal, Cristóbal Sifón, Edward J. Wollack, Maria Salatino, Joel N. Ullom, Jeff Van Lanen, Alexander Van Engelen, Lukas Wenzl

Research output: Contribution to journalArticlepeer-review


We investigate the impact and mitigation of extragalactic foregrounds for the cosmic microwave background (CMB) lensing power spectrum analysis of Atacama Cosmology Telescope (ACT) data release 6 (DR6) data. Two independent microwave sky simulations are used to test a range of mitigation strategies. We demonstrate that finding and then subtracting point sources, finding and then subtracting models of clusters, and using a profile bias-hardened lensing estimator together reduce the fractional biases to well below statistical uncertainties, with the inferred lensing amplitude, A lens, biased by less than 0.2σ. We also show that another method where a model for the cosmic infrared background (CIB) contribution is deprojected and high-frequency data from Planck is included has similar performance. Other frequency-cleaned options do not perform as well, either incurring a large noise cost or resulting in biased recovery of the lensing spectrum. In addition to these simulation-based tests, we also present null tests on the ACT DR6 data for sensitivity of our lensing spectrum estimation to differences in foreground levels between the two ACT frequencies used, while nulling the CMB lensing signal. These tests pass whether the nulling is performed at the map or bandpower level. The CIB-deprojected measurement performed on the DR6 data is consistent with our baseline measurement, implying that contamination from the CIB is unlikely to significantly bias the DR6 lensing spectrum. This collection of tests gives confidence that the ACT DR6 lensing measurements and cosmological constraints presented in companion papers to this work are robust to extragalactic foregrounds.

Original languageEnglish (US)
Article number138
JournalAstrophysical Journal
Issue number1
StatePublished - May 1 2024

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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