HIGH RESOLUTION SPECTROSCOPY OF QUASAR ABSORPTION LINES (INTERGALACTIC MEDIUM, EXTRAGALACTIC, GALAXIES).
AuthorBECHTOLD, JILL ELEANOR.
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PublisherThe University of Arizona.
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AbstractThis dissertation investigates the properties of the metal-containing absorption lines seen in quasar spectra which have Z(abs) < < Z(em). These systems, which probably originate in the halos of galaxies at high redshift, are then compared to observations of the halo and interstellar medium of the Milky Way. We obtained echelle spectra at the Multiple Mirror Telescope (MMT) of the Z = 1.79 absorption system of the quasar B2 1225+317. The velocity profiles showed complex structure which varied from ion to ion, with ionization and column densities varying from component to component. The relative colums were consistent with the expectations for approximately interstellar abundance, low density material, in equilibrium with the ultraviolet radiation field of a spiral galaxy for λ > 912 A, and the integrated light from QSOs at Z = 1.79 for λ < 912 A. The aggregate C IV profile has a width of about 450 km/sec, larger than that expected for a single galaxy halo, however. With the MMT spectrograph and echellette grating, and MMT echelle, we studied the properties of three other redshift systems of B2 1225+317, which are optically thin at the Lyman limit, but have saturated Lyman alpha, and unlike material in the Milky Way, have strong C IV and no detectable C II. In some cases Si III and Si IV are weakly detected. Constructing photoionization models, we derive low total densities, cloud diameters on the order of a few kiloparsecs, and abundances which are consistent with the interstellar values. We calculated the contribution of quasars to the UV radiation field as a function of redshift. The calculated field depends on a number of uncertain assumptions, which were varied in order to estimate their effect on the result. Finally, we discuss an important input into these calculations, the continuum spectral energy distribution for quasars, with particular attention to the extreme ultraviolet.