A hybrid map-Cℓ component separation method for primordial CMB B-mode searches

• Published in: Journal of cosmology and astroparticle physics Vol. 2023; no. 3; pp. 035 - 62
• Main Authors: Azzoni, S., Alonso, D., Abitbol, M.H., Errard, J., Krachmalnicoff, N.
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 01.03.2023
• Subjects: CMBR experiments; CMBR polarisation; Cosmic microwave background; cosmological parameters from CMBR; gravitational waves and CMBR polarization; Ionization; Mathematical analysis; Observatories; Separation; Tensors
• ISSN: 1475-7516; 1475-7516
• DOI: 10.1088/1475-7516/2023/03/035

The observation of the polarised emission from the Cosmic Microwave Background (CMB) fromfuture ground-based and satellite-borne experiments holds the promise of indirectly detecting theelusive signal from primordial tensor fluctuations in the form of large-scale B-modepolarisation. Doing so, however, requires an accurate and robust separation of the signal frompolarised Galactic foregrounds. We present a component separation method for multi-frequency CMBobservations that combines some of the advantages of map-based and power-spectrum-basedtechniques, and which is direcly applicable to data in the presence of realistic foregrounds andinstrumental noise. We demonstrate that the method is able to reduce the contamination fromGalactic foregrounds below an equivalent tensor-to-scalar ratio rFG ≲ 5 × 10-4, as required for next-generation observatories, for a wide range offoreground models with varying degrees of complexity. This bias reduction is associated with amild ∼20–30% increase in the final statistical uncertainties, and holds for largesky areas, and for experiments targeting both the reionisation and recombination bumps in theB-mode power spectrum.