Jason Xavier Prochaska

METALLICITY EVOLUTION IN THE EARLY UNIVERSE

Observations of the damped Lyalpha systems provide direct measurements on the chemical enrichment history of neutral gas in the early universe. In this Letter, we present new measurements for four damped Lyalpha systems at high redshift. Combining these data with [Fe/H] values culled from the literature, we investigate the metallicity evolution of the universe from z approximately 1.5 to 4.5. Contrary to our expectations and the predictions of essentially every chemical evolution model, the N(H i)-weighted mean [Fe/H] metallicity exhibits minimal evolution over this epoch. For the individual systems, we report tentative evidence for an evolution in the unweighted [Fe/H] mean and the scatter in [Fe/H], with the higher redshift systems showing lower scatter and lower typical [Fe/H] values. We also note that no damped Lyalpha system has &sqbl0;Fe&solm0;H&sqbr0;<-2.7 dex. Finally, we discuss the potential impact of small number statistics and dust on our conclusions and consider the implications of these results on chemical evolution in the early universe.

An 84-μG magnetic field in a galaxy at redshift z = 0.692

The magnetic field pervading our Galaxy is a crucial constituent of the interstellar medium: it mediates the dynamics of interstellar clouds, the energy density of cosmic rays, and the formation of stars. The field associated with ionized interstellar gas has been determined through observations of pulsars in our Galaxy. Radio-frequency measurements of pulse dispersion and the rotation of the plane of linear polarization, that is, Faraday rotation, yield an average value for the magnetic field of B ≈ 3 μG (ref. 2). The possible detection of Faraday rotation of linearly polarized photons emitted by high-redshift quasars suggests similar magnetic fields are present in foreground galaxies with redshifts z > 1. As Faraday rotation alone, however, determines neither the magnitude nor the redshift of the magnetic field, the strength of galactic magnetic fields at redshifts z > 0 remains uncertain. Here we report a measurement of a magnetic field of B ≈ 84 μG in a galaxy at z = 0.692, using the same Zeeman-splitting technique that revealed an average value of B = 6 μG in the neutral interstellar gas of our Galaxy. This is unexpected, as the leading theory of magnetic field generation, the mean-field dynamo model, predicts large-scale magnetic fields to be weaker in the past rather than stronger.

Baryons: What,When and Where?

We review the current state of empirical knowledge of the total budget of baryonic matter in the Universe as observed since the epoch of reionization. Our summary examines on three milestone redshifts since the reionization of H in the IGM, z = 3, 1, and 0, with emphasis on the endpoints. We review the observational techniques used to discover and characterize the phases of baryons. In the spirit of the meeting, the level is aimed at a diverse and non-expert audience and additional attention is given to describe how space missions expected to launch within the next decade will impact this scientific field.

An 84-μG Magnetic Field in a Galaxy at Z=0.692?

Arthur M. Wolfe1, Regina A. Jorgenson1, Timothy Robishaw2, Carl Heiles2, and Jason X. Prochaska3 Dept. of Physics and Center for Astrophysics and Space Sciences University of California, San Diego La Jolla, CA 92093-0424, USA email: awolfe@ucsd.edu, regina@physics.ucsd.edu Astronomy Department, University of California Berkeley, CA 94720-3411, USA email: robishaw@astro.berkeley.edu, heiles@astro.berkeley.edu UCO-Lick Observatory, University of California, Santa Cruz Santa Cruz, CA 95464, USA email: xavier@ucolick.org