The observational methods for detecting and measuring extragalactic magnetic fields are discussed, along with some new indirect methods which could be used for inferring field strengths at large redshifts which are otherwise beyond the reach of direct measurement. Various cosmological seed field generation mechanisms are reviewed, which could generate seed fields for the subsequently formed galaxies. The question of whether the original seed fields were produced in galaxies, or the pre-recombination early Universe must await a clearer picture of how the first stars and galaxies formed.

https://iopscience.iop.org/article/10.1088/0034-4885/57/4/001/pdf

Extragalactic magnetic fields

Magnetic fields are important in the Universe and their effects contain the key to many astrophysical phenomena that are otherwise impossible to understand. This book presents an up-to-date overview of this fast-growing topic and its interconnections to plasma processes, astroparticle physics, high energy astrophysics, and cosmic evolution. The phenomenology and impact of magnetic fields are described in diverse astrophysical contexts within the Universe, from galaxies to galaxy clusters, the filaments and voids of the intergalactic medium, and out to the largest redshifts. The presentation of mathematical formulae is accessible and is designed to add insight into the broad range of topics discussed. Written for graduate students and researchers in physics, astrophysics and related disciplines, this volume will inspire readers to devise new ways of thinking about magnetic fields in space on galaxy scales and beyond.

Cosmic Magnetic Fields

A reliable determination of the Faraday rotation in our Galaxy at the higher galactic latitudes has enabled us, for the first time, to accurately subtract it from the measured Faraday rotation measures (RM’s) of distant extragalactic radio sources. The difference, or “residual rotation measure” (RRM) has been used to investigate two basic phenomena and their interpretation: These are (1) the relationship between the extragalactic Faraday rotation of quasars and the characteristics of their optical spectra, where such exist with sufficient quality, and (2), the variation with redshift of the RRM of quasars. In this paper, I shall briefly review the evidence supporting the first detection of large scale magnetic fields in the universe out to redshifts of 2 and greater. I shall also show some independent, new evidence which gives us some further, more direct clues concerning the nature of the extragalactic systems containing the magnetic fields which I and my collaborators have detected.

Magnetic Fields and Faraday-Active Clouds out to the Distances of Quasars

We have tried to determine the rate of chemical evolution of high redshift galaxies from the observed redshift distribution of the heavy element absorption systems in the spectra of QSOs, taking into account the evolution in the intensity of the metagalactic UV ionizing radiation background, the radius and/or the co-moving number density of, and the fraction of mass in the form of gas in, the absorbers. The data for both the Lyman limit systems and the C IV systems have been fitted simultaneously. It seems that the abundance of carbon has possibly increased by about a factor of 5 to 20 from the cosmic time corresponding to the redshift ≃ 4 to 2. The data also suggest that either the radius or the co-moving number density of the galaxies increased with redshift up to z = 2.0 and decreased slowly thereafter. The total mass of the halo gas was higher in the past, almost equal to the entire mass of the galaxy at z = 4. The hydrogen column density distribution for Lyman limit systems predicted by the model is in agreement with the observed distribution.

Chemical Evolution of High Redshift Galaxies

Chemical evolution of the high redshift galaxies

/pdf/cosmological-implications-of-the-redshift-distribution-of-4s0ywnrr95.pdf

Judith J. Perry

Papers

Cosmological implications of the redshift distribution of QSO absorption systems.