Other
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt.........5o&link_type=abstract
Thesis (PH.D.)--UNIVERSITY OF CALIFORNIA, SAN DIEGO, 1995.Source: Dissertation Abstracts International, Volume: 56-06, Section:
Other
Magnetic Fields
Scientific paper
We investigate whether magnetic fields are present in distant galaxies by searching for a correlation between Faraday rotation and absorption in quasar lines of sight. We present a survey of Faraday rotation for 61 radio-bright quasars, of which eleven are known to exhibit damped Lyalpha absorption. The rate of incidence of significant Faraday rotation for these eleven sources is compared to the remaining 50 and is found to be higher at the 99.8% confidence level. However, as this is based upon only two detections in the damped Ly alpha sample, the result is only tentative. The inferred rotation measure induced by these systems is roughly 250 rm radċm^ {-2}. The detections were for the two lowest redshift absorbers in the sample. A rotation measure of 250 rm radċm^ {-2} would have gone undetected for any other absorber in the damped Lyalpha sample due to redshift dilution of the observed Faraday rotation. Thus the data are consistent with, but do not prove, the hypothesis that Faraday rotation is a generic property of damped Lyalpha absorbers. We do not confirm the suggestion that the amplitude of extragalactic Faraday rotation increases with redshift. Rather, the data are consistent with no redshift evolution. We present an optical survey of 48 quasars suitable for detecting Mg II absorption. Combining this data with data from the literature and comparing the rotation measures of quasars which show Mg II absorption in their spectra to those which do not, we find no evidence for an excess of Faraday rotation in Mg II absorption systems. We establish an upper limit of 200 rm radċm^{-2} for the root-mean -square intrinsic rotation measure in these systems, assuming that these rotation measures are drawn from a normal distribution which does not evolve with redshift. The implied magnetic field strength per cloud in a Mg II absorption system is less than about 10 muG. The uncertainty in the estimation of the Galactic rotation measure is a more serious problem than previously realized for extragalactic Faraday rotation studies such as this one. The Galactic rotation measure can only be determined to an accuracy of about 15 to 20 rm radċm^{-2}.
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