MSc defense by Rikke Saust – University of Copenhagen

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MSc defense by Rikke Saust

Title: Investigating the Nature of Damped Lyman-α Absorbing Galaxies

Supervisor: Lise Christensen (DARK)

Abstract: This thesis focuses on investigating the physical conditions in galaxies as absorbers. A part of the thesis focuses on the Damped Lyman-α Absorbing systems, DLAs, which give important insights into the properties of galaxies, especially at high redshifts. A sample of 85 quasars observed with X-shooter on the Very Large Telescope has been searched for DLAs. This has resulted in identification of 33 high redshift DLAs. From the important property that the metallicity is related to the kinematics of DLAs, a mean metallicity for the DLA sample was found to be [M/H]=-1.8 dex by measuring the equivalent width of SiII 1526. DLAs are high column density neutral gas absorbers and contribute significantly to the cosmological mass density of neutral gas, which is connected to the star formation in galaxies. In order to contribute to previous studies of the cosmological mass density of neutral gas for DLAs, ΩDLA, it was estimated for a sub-sample of the identified high redshift DLAs. The result is ΩgDLA=0.00167 ± 0.00069 at a redshift interval of z = [3.22, 4.47], consistent with previous studies.

Another part of the thesis focuses on two low redshift galaxies(NGC-4193 and UGC-08066) near the sight-line of background quasars. Observations with long-slit spectra which cover both quasar and galaxy have been processed and analysed. Via emission line diagnostics the metallicity was measured across the galaxies and the radial metallicity gradients were found to be quite flat. Given that the metallicities was found to be around solar values, it is predicted that solar metallicity absorbing systems might be seen in the background quasar spectra. However, this has to be confirmed with ultra-violet data of the quasars. The line diagnostics also showed sign of shock ionization, possibly explained by bar shocks.

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