Polarization profile for different subsets of photons. In all the plots, the red solid line is the median profile; the red dashed lines are the first and third quartiles. The thin grey lines represent the profiles for a) 100 LOS with the same photons subset for the gas emission; b) 100 different photon subsets seen with the same LOS for the gas emission; c) 100 LOS with the same photon subsets for the galactic emission; d) 100 different photon subsets seen with the same LOS for the galactic emission.