Peeling off foregrounds with the constrained moment ILC method to unveil primordial CMB $B$-modes

Understand

Galactic foregrounds are the main obstacle to observations of the cosmic microwave background (CMB) $B$-mode polarization.

• In addition to obscuring the inflationary $B$-mode signal by several orders of magnitude, Galactic foregrounds have non-trivial spectral signatures that are partially unknown and distorted by averaging effects along the line-of-sight, within the pixel/beam window, and by various analysis choices (e.g., spherical harmonic transforms and filters).
• Statistical moment expansion methods provide a powerful tool for modeling the effective Galactic foreground emission resulting from these averaging effects in CMB observations, while blind component separation treatments can handle unknown foregrounds.
• In this work, we combine these two approaches to develop a new semi-blind component separation method at the intersection of parametric and blind methods, called constrained moment ILC (cMILC).