Say I have a flux density spectrum of a galaxy, as well as polarization spectra for the object in U, Q, and P. I want to find the polarization of some emission line in the spectrum. First, I can fit a line to my flux spectrum which will give me the continuum (i.e. without the peak(s)). I can then subtract the continuum from the whole spectrum to get just the profile of the emission line. But I'm unclear on how to relate these results with the polarization spectrum (right now I'm just working with the Q). I'm guessing I need to subtract the continuum polarization from my polarization spectrum, which would also involve converting my flux continuum to some polarization units, but how do I do this? Do I need the U or P (total) portion as well to do this?