Date of Award


Document Type

Open Access Thesis


Physics and Astronomy

First Advisor

Varsha Kulkarni


In order to gain a complete understanding of galaxy formation and evolution, knowledge of the atomic and molecular gas in the interstellar medium (ISM) is required. Absorption-line spectroscopy of quasars offers a powerful and luminosity independent probe of gas in distant galaxies. The Damped Lyman- systems (DLAs; 20.3 . log NHI ), are the highest neutral hydrogen column density quasar absorbers and contain a substantial fraction of the neutral gas available for star formation in the high-redshift Universe. This thesis presents a study of the metal content in some DLAs, based on optical spectroscopy, and a search for molecules based on sub-mm observations. For the sub-mm sample, spectra for 5 quasars with absorbers (0.524 < zabs < 1.173) were taken with SPIRE and Heterodyne Instrument for the far-infrared (HIFI) on Herschel. These observations, in the far-IR and sub-mm bands, were optimized for detection of molecular lines of CO, 13CO, C18O, H2O, HCO, and the forbidden transitions of [C II] and [N II]. Two targets, the DLA towards PKS0420-014 at z = 0.633 and the DLA towards AO0235+164 at z = 0.524, showed very tentative detections of C18O, and another, the DLA towards TXS0827+243 at z = 0.52476, showed a very tentative detection HCO. We report 3 upper limits for several other molecules. Two especially gas-rich DLAs (“super-DLAs”) with z = 2.5036 and z = 2.045 were observed using the echellette mode on Keck Echellette Spectrograph and Imager (ESI). These observations were optimized to detect a number of metal lines. Both absorbers show remarkably similar metallicities of ~ −1.3 to ~ −1.4 dex and comparable, definitive depletion levels, as judged from [Fe/Zn] and [Ni/Zn]. One of the absorbers shows supersolar [S/Zn] and [Si/Zn]. Using potential detections of weak Ly- emission at the bottom of the DLA trough for Q0230-0334, we estimate star formation rates in the absorbers to be ~1.6 Myr −1. Finally, measurements of the absorption line velocity spread, v90, suggest that super-DLAs may have narrower velocity dispersions and may arise in cooler and/or less turbulent gas.


© 2015, Sean Stephen Morrison

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