J Xavier Prochaska

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Accepted —. Received —; in original form — ABSTRACT An experimental search for variation in the fundamental coupling constants is strongly motivated by modern high-energy physics theories. Comparison of quasar absorption line spectra with laboratory spectra provides a sensitive probe for variability of the fine structure constant, α, over cosmological(More)
Comparison of quasar absorption spectra with laboratory spectra allow us to probe possible variations in the fundamental constants over cosmological timescales. In a companion paper we present an analysis of Keck/HIRES spectra and report possible evidence suggesting that the fine structure constant, α, may have been smaller in the past: ∆α/α = (−0.72 ±(More)
Comparison of quasar absorption line spectra with laboratory spectra provides a precise probe for variability of the fine structure constant, α, over cosmological timescales. We constrain variation in α in 21 Keck/HIRES Si iv absorption systems using the alkali doublet (AD) method in which changes in α are related to changes in the doublet spacing. The(More)
We present first results from a program to measure the chemical abundances of a large (N > 30) sample of thick disk stars with the principal goal of investigating the formation history of the Galactic thick disk. We have obtained high resolution, high signal-to-noise spectra of 10 thick disk stars with the HIRES spectrograph on the 10m Keck I telescope. Our(More)
We present new chemical abundance measurements of 16 damped Lyα systems at z > 1.5 and update our previous abundance analyses. The entire database presented here was derived from HIRES observations on the Keck I telescope, reduced with the same software package, and analysed with identical techniques. Altogether, we present a large, homogeneous database of(More)
This paper describes the acquisition and analysis of imaging data for the identification of galaxies associated with z ∼ 4 damped Lyα systems. We present deep BRI images of three fields known to contain four z ∼ 4 damped systems. We discuss the reduction and calibration of the data, detail the color criteria used to identify z ∼ 4 galaxies, and present a(More)
We investigate the ionization state of the damped Ly system at z ¼ 2:62 toward GB 1759+7539 through an analysis of ionic ratios sensitive to photoionization: Ar 0 /mately half of the metals arise in a mostly neutral velocity component with H i/H > 0:9, based on Fe þþ =Fe þ < 0:013. In contrast, the remaining half exhibit Fe þþ =Fe þ % 0:3, indicative of a(More)
We compare new observations on the kinematic characteristics of the damped Lyα systems against results from numerical SPH simulations to test the predictions of hierarchical galaxy formation. This exercise is particularly motivated by recent numerical results on the cross-section of damped Lyα systems. Our analysis focuses on the velocity widths ∆v of ≈ 50(More)
This paper presents chemical abundance measurements for 37 damped Lyα systems at z > 2.5 observed with the Echellette Spectrograph and Imager on the Keck II telescope. We measure the H I column densities of these damped systems through Voigt profile fits to their Lyα profiles and we implement the apparent optical depth method to determine ionic column(More)
We publish the Keck / HIRES and Keck / ESI spectra that we have obtained during the first 10 years of Keck observatory operations. Our full sample includes 42 HIRES spectra and 39 ESI spectra along 65 unique sight lines providing abundance measurements on %85 DLA systems. The normalized data can be downloaded from the journal or from our supporting Web(More)