Characterizing line-of-sight variability of polarized dust emission with future CMB experiments

Understand

Galactic dust emission is often accounted for in cosmic microwave background (CMB) analyses by fitting a simple two-parameter modified blackbody (MBB) model in each pixel, which nominally accounts for the temperature and opacity of the dust.

• While this may be a good approximation for individual dust clouds, typically a number of such clouds are found along each line of sight and within each angular pixel, resulting in a superposition of their spectra.
• In this paper, we study the effects of this superposition on pixel-based foreground fitting strategies by modelling the spectral energy distribution (SED) in each pixel as the integral of individual MBB spectra over various physically-motivated statistical distributions of dust cloud properties.
• We show that fitting these SEDs with the simple two-parameter MBB model generally results in unbiased estimates of the CMB Stokes Q and U amplitudes in each pixel, unless there are significant changes in both the dust SED and polarization angle along the line of sight, in which case significant ($ > 10\sigma$) biases are observed in an illustrative model.