Milli-arcsecond scale rotation measure in the CSS quasars 0548+165 and 1524 136

Two Compact Steep-spectrum Sources (CSSs), 0548+165 and 1524 136, chosen from a list of CSSs with polarization percentages that decrease with decreasing frequency and high rotation measure values (RM > 450 rad m 2 ) on arcsecond scales, were observed with the VLBA at 4.9 and 8.4 GHz. RM values up to10 4 rad m 2 were found in several regions along the jets in both sources. We suggest that a thin screen of magneto-ionic material with about 1 kpc thickness is responsible for these high RMs. The observed depolarization may be due to beam depolarization and/or inhomogeneities in the magnetic eld.