Study of Fararday RM in Magellanic clouds

We introduce a simple test using Galactic diffuse polarized emission that evaluates whether structures evident in RM observations are associated with distant circumgalactic medium or foreground interstellar medium. We focus on the Magellanic Leading Arm region where a clear excess of RM was previously reported.

There are two gaseous objects standing out in this direction: the distant Magellanic Leading Arm and the nearby Antlia supernova remnant (SNR). We recognized narrow depolarized filaments in the 2.3 GHz S-band Polarization All Sky Survey image that overlaps with the reported RM excess. We suggest that there is a steep gradient in Faraday rotation in a foreground screen arising from the Antlia SNR.