RM structure functions evaluated in the H I tail (black) and in the control region (magenta). The gray lines near the control region are the best-fit simulated RM structures reported in Fig. 6. Those near the H I tail region are best-fit models for the H I tail excess obtained considering that the observed RM at the H I position is due to the intrinsic H I tail contribution plus the RM model of the control region. The best-fit parameters are reported on the left.