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tokens: intrinsic to the sources, while intervening material introduces a small but pervasive broadening of the FD distribution. We explore further the implications of the latter effect in Section 6. Further exploration of the properties of the background sources from QU-fitting (O’Sullivan et al. 2012 ; Sun et al. 2015 ) and analysis of the shape of the plots is beyond the scope of the current work, but we plan to develop this further in the future. The results of the QU-fitting will also be very interesting to be compared with . 6. DISCUSSION In this section, we will try to be more quantitative about the size of the Faraday Effects that are associated with the presence of intervening material, as revealed by Mg ii absorption. This will enable us to better characterize the physical properties of this material. We estimate the dispersion of φ introduced by intervening systems. The largest separation in the empirical distribution functions for sources with and without interveners is observed at m −2 . As noted earlier, this value should be treated with caution because the φ resolution limit of our experiment is roughly m −2 for VLA and m −2 for ATCA. The difficulties of the RMSF can to a certain degree be circumvented by simply subtracting in quadrature the median of sources with and without absorbers (since the RMSF has been subtracted from both equally). This yields an estimate for the excess m −2 . The maximum separation seen in the distribution is at m −2 . However, here this value should also be treated with caution because of the non-monotonic structure in and the rather ad hoc approach to choosing the wavelength range for the fit (only longwards of the peak in polarization). Likewise, subtracting the median values of the distribution with and without absorbers in quadrature gives an estimate for the excess m −2 . and attempt to trace by different approaches. The fact that their values are similar gives some confidence that the proposed scenario is self-consistent. From the current work, we will use a value of order 10 rad m −2 as a crude order of magnitude estimate of the FD dispersion that is associated with intervening systems. This is an estimate of the range of the observed φ within (i.e., across the face of) a given intervening system. To convert to the rest-frame of the absorber, we must multiply by , i.e., by a factor of the order of two for our median absorber redshift of , yielding of the order of m −2 . This value is of the same order of magnitude as the spread in Galactic RMs m −2 as estimated by Schnitzeler ( 2010 ). Other works have claimed m −2 for the Large Magellanic Cloud (Gaensler et al. 2005 ) and m −2 for the Small Magellanic Cloud (Mao et al. 2008 ). As in Bernet et al. ( 2008 ), we can crudely associate a φ with an estimate of magnetic field strength using an estimate of the free electron column density in the interveners based on the known Mg ii column density. Assuming a compact absorber system at redshift z and the