Interstellar Polarization Survey III: Relation Between Polarization and Extinction in diffuse interstellar medium fields
The dust extinction and the degree of polarization are complementary tracers of the Galactic magnetic field (GMF) in the interstellar medium (ISM). The degree of linear polarization as a function of the extinction, P/Av also known as polarization efficiency, measures the fraction of dust-grains that are polarizing and the slope of its envelope differs for different grain/magnetic field properties. The Serkowski (1975) empirical value for this relation was P/E(B-V) ≲ 9, where Av/E(B-V)=3.1 is considered. Fosalba et al. (2002) found consistency with this limit but a best-fit of P = 3.5 E(B-V)^0.8, while Planck Collaboration (2018, XII) found very high polarized regions and constrained the upper envelope to P/E(B-V) = 13. Furthermore, Panopoulou et al. (2019) showed evidence that the polarization efficiency upper limit has not been very well constrained yet, therefore, we use new data of diffuse ISM from the IPS survey (see Versteeg et al. Poster) to check if such relation varies across the sky. Preliminary results have shown that it is possible to obtain higher values of the upper envelope in some regions of the sky (b ≿ 13°) where the GMF lines are approximately perpendicular to the line-of-sights and such upper limits seem to be highly dependent on the extinction map.
