We probed the magnetic fields in high-redshift galaxies using excess extragalactic contribution to residual rotation measure (RRM) for quasar sightlines with intervening MgII absorbers. Based on a large sample of 1132 quasars, we have computed RRM distributions broadening using median absolute deviation from the mean ({sigma}rrm^md^), and found it to be 17.1+/-0.7rad/m^2^ for 352 sightlines having MgII intervening absorbers in comparison to its value of 15.1+/-0.6rad/m^2^ for 780 sightlines without such absorbers, resulting in an excess broadening ({sigma}rrm^ex^) of 8.0+/-1.9rad:m^2^ among these two subsamples. This value of {sigma}rrm^ex^, has allowed us to constrain the average strength of magnetic field (rest frame) in high-redshift galaxies responsible for these Mg II absorbers, to be ~1.3+/-0.3{mu}G at a median redshift of 0.92. This estimate of magnetic field is consistent with the reported estimate in earlier studies based on radio-infrared correlation and energy equipartition for galaxies in the local universe. A similar analysis on subsample split based on the radio spectral index, {alpha} (with F_{nu}{propto}{nu}^{alpha}^), for flat ({alpha}>=-0.3; 315 sources) and steep ({alpha}<=-0.7; 476 sources) spectrum sources shows a significant {sigma}_rrm^ex^ (at 3.5{sigma} level) for the former and absent in the latter. An anticorrelation found between the {sigma}rrm^md^ and percentage polarization (p) with a similar Pearson correlation of -0.62 and -0.87 for subsamples with and without MgII, respectively, suggests the main contribution for decrements in the p value to be intrinsic to the local environment of quasars.

Cone search capability for table J/ApJ/890/132/table2 (Main properties of our 1132 quasars (after discounting 3 outliers being at 9{sigma} level))