Spectral Imaging with QUBIC: building frequency maps from Time-Ordered-Data using Bolometric Interferometry

TL;DR

This paper introduces a spectral-imaging method for Bolometric Interferometry, enabling frequency map reconstruction from time-ordered data to improve foreground removal in CMB polarization studies.

Contribution

The novel spectral-imaging technique leverages the instrument's physical bandwidth and beam shape evolution to reconstruct sub-frequency maps from time domain data.

Findings

Reconstructed unbiased sub-frequency maps with spectral-imaging capacity.

Achieved a forecast tensor-to-scalar ratio constraint of σ(r)=0.0225.

Demonstrated the method's effectiveness through end-to-end simulations.

Abstract

The search for relics from the inflation era in the form of B-mode polarization of the CMB is a major challenge in cosmology. The main obstacle appears to come from the complexity of Galactic foregrounds that need to be removed. Multi-frequency observations are key to mitigating their contamination and mapping primordial fluctuations. We present spectral-imaging, a method to reconstruct sub-frequency maps of the CMB polarization within the instrument's physical bandwidth, a unique feature of Bolometric Interferometry that could be crucial for foreground mitigation as it provides an increased spectral resolution. Our technique uses the frequency evolution of the shape of the Bolometric Interferometer's synthesized beam to reconstruct frequency information from the time domain data. We reconstruct sub-frequency maps using an inverse problem approach based on detailed modeling of the instrument acquisition. We use external data to regularize the convergence of the estimator and account for bandpass mismatch and varying angular resolution. The reconstructed maps are unbiased and allow exploiting the spectral-imaging capacity of QUBIC. Using end-to-end simulations of the QUBIC instrument, we perform a cross-spectra analysis to extract a forecast on the tensor-to-scalar ratio constraint of $\sigma(r)= 0.0225$ after component separation.