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We present chemical abundance measurements from high-resolution observationsof 5 sub-damped Lyman-alpha absorbers at 1.7 < z < 2.4 observed with theMagellan Inamori Kyocera Echelle (MIKE) spectrograph on the 6.5-m Magellan IIClay telescope. Lines of Zn II, Mg I, Mg II, Al II, Al III, S II, Si II, Si IV,C II, C II*, C IV, Ni II, Mn II and Fe II were detected and column densitieswere determined. The metallicity of the absorbing gas, inferred from the nearlyundepleted element Zn, is in the range of < -0.95 to +0.25 dex for the fiveabsorbers in our sample, with three of the systems being near-solar orsuper-solar. We also investigate the effect of ionisation on the observedabundances using photoionisation modelling. Combining our data with othersub-DLA and DLA data from the literature, we report the most complete existingdetermination of the metallicity vs. redshift relation for sub-DLAs and DLAs.We confirm the suggestion from previous investigations that sub-DLAs are, onaverage, more metal-rich than DLAs and evolve faster. We also discuss relativeabundances and abundance ratios in these absorbers. The more metal-rich systemsshow significant dust depletion levels, as suggested by the ratios [Zn/Cr] and[Zn/Fe]. For the majority of the systems in our sample, the [Mn/Fe] vs. [Zn/H]trend is consistent with that seen previously for lower-redshift sub-DLAs. Wealso measure the velocity width values for the sub-DLAs in our sample fromunsaturated absorption lines of Fe II 2344, 2374, 2600 A, and examine wherethese systems lie in a plot of metallicity vs. velocity dispersion. Finally, weexamine cooling rate vs. H I column density in these sub-DLAs, and compare thiswith the data from DLAs and the Milky Way ISM. We find that most of the systemsin our sample show higher cooling rate values compared to those seen in theDLAs.

Element Abundances at High-redshift: Magellan MIKE Observations of sub-Damped Lyman-alpha Absorbers at 1.7 < z <2.4