MAGNETIC-FIELD STRENGTHS IN HIGH-REDSHIFT GALAXIES - CAN THE GALACTIC DYNAMO BE TESTED

We examine the hypothesis that the population of strong H I absorption systems is responsible for a significant excess Faraday rotation measure in quasars, and conclude that the case is unproved, in contrast to a recent analysis by Wolfe, Lanzetta, & Oren (1991). We discuss the limitations and pitfalls inherent in attempts to derive firm magnetic field strengths from the existing integrated rotation measures of quasars, and we show that although it is premature to use integrated quasar rotation measures to either confirm or rule out particular mechanisms of magnetic field amplification in galaxy disks, our observations may call for reexamination of current theories of large-scale magnetic field generation. We discuss the sources of rotation measure in the double quasar 0957+561. Because of the uncertainties in the determination of the magnetoionic properties of high-redshift systems which we discuss, it is important that preliminary results should not be over- or misinterpreted and that caution should be exercised before attempting to tie these results to fundamental physical processes connected with galaxy formation and the early universe.