KECK AND VLT OBSERVATIONS OF SUPER-DAMPED Ly alpha ABSORBERS AT z similar to 2-2.5: CONSTRAINTS ON CHEMICAL COMPOSITIONS AND PHYSICAL CONDITIONS

International audienceWe report Keck/Echellette Spectrograph and Imager and Very Large Telescope/Ultraviolet-Visual Echelle Spectrograph observations of three super-damped Ly alpha quasar absorbers with H I column densities log N-H I \textgreater= 21.7 at redshifts 2 less than or similar to z less than or similar to 2.5. All three absorbers show similar metallicities (similar to-1.3 to -1.5 dex), and dust depletion of Fe, Ni, and Mn. Two of the absorbers show supersolar [S/Zn] and [Si/Zn]. We combine our results with those for other damped Ly alpha a absorbers (DLAs) to examine trends between N-H I, metallicity, and dust depletion. A larger fraction of the super-DLAs lie close to or above the line [X/H] = 20.59 - log N-H I in the metallicity versus N-H I plot, compared to the less gas-rich DLAs, suggesting that super-DLAs are more likely to be rich in molecules. Unfortunately, our data for Q0230-0334 and Q0743+1421 do not cover H-2 absorption lines. For Q1418+0718, some H-2 lines are covered, but not detected. CO is not detected in any of our absorbers. For DLAs with log N-H I \textless 21.7, we confirm strong correlation between metallicity and Fe depletion, and find a correlation between metallicity and Si depletion. For super-DLAs, these correlations are weaker or absent. The absorbers toward Q0230-0334 and Q1418+0718 show potential detections of weak Ly alpha emission, implying star formation rates of similar to 1.6 and similar to 0.7M(circle dot) yr(-1), respectively (ignoring dust extinction). Upper limits on the electron densities from C (II) */C (II) or Si (II) */ Si (II) are low, but are higher than the median values in less gas-rich DLAs. Finally, systems with log N-H I \textgreater 21.7 may have somewhat narrower velocity dispersions Delta v(90) than the less gas-rich DLAs, and may arise in cooler and/or less turbulent gas