Polarization angle accuracy for future CMB experiments

The COSMOCal project and its prototype in the 1 mm band

¹ INAF-Osservatorio Astronomico di Cagliari, Via della Scienza 5, 09047 Selargius, IT
² Laboratoire de Physique de l’École Normale Supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université de Paris, 75005 Paris, France
³ Department of Physics, Università di Milano-Bicocca, Piazza della Scienza, 3, 20126, Milan, Italy
⁴ IAS, CNRS, Universitè Paris-Saclay, CNRS, Bât. 121, 91405 Orsay, France
⁵ LERMA, Observatoire de Paris - PSL, 61 Avenue de l’Observatoire, 75014 Paris, France
⁶ Univ. Grenoble Alpes, CNRS, LPSC-IN2P3, 53, avenue des Martyrs, 38000 Grenoble, France
⁷ CENSUS, Observatoire de Paris - PSL, Université PSL, 92195 Meudon, France
⁸ Dipartimento di Fisica, Sapienza Università di Roma, 00185 Roma, Italy
⁹ Institut d’Astrophysique de Paris, CNRS & Sorbonne Université (UMR7095), 75014 Paris, France
¹⁰ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
¹¹ Université Grenoble Alpes, CNRS, Institut Néel, France
¹² Université Paris Cité, CNRS, Astroparticule et Cosmologie, F-75013 Paris, France
¹³ Université de Toulouse, UPS-OMP, CNRS, IRAP, 31028 Toulouse, France
¹⁴ Institut de Radioastronomie Millimétrique (IRAM), 38406 Saint Martin d’Hères, France

^* e-mail: alessia.ritacco@inaf.it

Published online: 28 March 2024

Abstract

The Cosmic Microwave Background (CMB) radiation offers a unique window into the early Universe, facilitating precise examinations of fundamental cosmological theories. However, the quest for detecting B-modes in the CMB, predicted by theoretical models of inflation, faces substantial challenges in terms of calibration and foreground modeling. The COSMOCal (COsmic Survey of Millimeter wavelengths Objects for CMB experiments Calibration) project aims at enhancing the accuracy of the absolute calibration of the polarization angle ψ of current and future CMB experiments. The concept includes the build of a very well known artificial source emitting in the frequency range [20-350] GHz that would act as an absolute calibrator for several polarization facilities on Earth. A feasibility study to place the artificial source in geostationary orbit, in the far field for all the telescopes on Earth, is ongoing. In the meanwhile ongoing hardware work is dedicated to build a prototype to test the technology, the precision and the stability of the polarization recovering in the 1 mm band (220-300 GHz). High-resolution experiments as the NIKA2 camera at the IRAM 30m telescope will be deployed for such use. Once carefully calibrated (Δψ < 0.1◦) it will be used to observe astrophysical sources such as the Crab nebula, which is the best candidate in the sky for the absolute calibration of CMB experiments.