The Low Ionization Gaseous Content in Intermediate Redshift Galaxies

Chris Churchill
University of California, Santa Cruz (1997)

Steven S. Vogt (chair, ucsc)
Frank D. Drake (seti)
Kenneth M. Lanzetta (suny, stonybrook) [Ken. Get a web page- its the year 2011, sheesh!)
Charles C. Steidel (caltech)
Dennis Zaritsky (arizona/steward)


The kinematic, chemical, and ionization conditions and spatial distributions of low ionization gas associated with early epoch galaxies have been studied using high resolution (6.6 km/s) absorption line spectra. The absorption profiles for a total of 48 Mg II selected systems were obtained from 25 quasar (QSO) spectra observed with the HIRES spectrograph on the Keck I telescope. In addition to the Mg II (2796,2803) doublet, also observed were the Mg I (2853) transition and multiple transitions of Fe II. In some cases, Mn II and Ca II were detected. The absorption profiles were objectively searched for weak absorbing subsystems. For each overall system, and for each of their multiple subsystems, absorption properties were measured directly from the flux values in the spectra. Additionally, the systems were fitted by Voigt Profile (VP) decomposition using an algorithm written for this work. Extensive simulations of the VP decomposition were performed in order to establish confidence levels on inferences based upon VP profile fits.

Main results include: (1) "High velocity" subsystems exhibit rest-frame equivalent widths less than 0.1 A and velocity widths less than 10 km/s. There is no evidence of a turnover in the equivalent widths of these subsystems down to 0.005 A. Thus, no lower limit on the size and column density of the clouds has been found to this limit. (2) The individual cloud temperatures are roughly 30,000 K and they are relatively quiescent in that they are consistent with having a zero non-thermal broadening component. (3) The power-law slope of the column density distributions for Mg II, Fe II, and Mg I were measured to be -1.58, -1.65, and -2.22. Within uncertainties, the Fe II slope is consistent with that of Mg II. (4) For a subsample of 15 systems, the number of absorbing clouds does not follow any trend with projected galactocentric distance, suggesting that the gas clouds are not distributed isothermally within galactic halos. (5) The spatial/kinematic model that is most consistent with the data is that in which the absorbing clouds are in an extended rotating disk with a surrounding diffuse infalling halo. The halo clouds are optically thin in H I and the dispersion in the disk is roughly 15 km/s.

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PASP Dissertation Abstract
Table of Contents
Ch 1. Introduction
Ch 2. Data Reduction & Analysis
Ch 3. The Absorbing Systems
Figs: Plots of the Data
Ch 4. Assessing VP Decomposition of HIRES Spectra
Ch 5. Column Densities, Line Broadening, and Kinematics
Ch 6. Exploring the Galaxy-Absorption Connection
Ch 7. Summary & Bibliography

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