A Keck HIRES Investigation of the Metal Abundances and Kinematics of Three Damped Lya Systems Toward Q2206-199

Abstract

We present high resolution, high SNR spectra of the QSO Q2206-199 obtained with HIRES on the 10m W.M. Keck Telescope. Our analysis focuses on the two previously identified damped \lya systems found at $z=1.920$ and $z=2.076$. For each system, we measure accurate abundances. The $z=1.920$ system exhibits the highest metallicity we have measured for a damped \lya system. We report the first confident ($>5 σ$) detection of Ti in a QSO absorption line system. By contrast the $z=2.076$ system is the most metal poor we have analyzed, showing absorption features for only the strongest transitions. We find no positive evidence for the presence of dust in either system. The two damped systems exhibit significantly different kinematic characteristics, yet we contend the two systems are consistent with one physical description: that of a thick, rotating disk. We investigate a very strong Mg II system at $z=0.752$ which is very likely yet a third damped \lya system. The very weak Mn II and Ti II transitions have been positively measured and imply $\log \N{HI} > 19.0$. We analyze the abundance ratios [Mn/Fe] and [Ti/Fe] and their values are inconsistent with dust depletion, yet consistent with the abundance pattern detected for halo stars in the Galaxy (see Lu et al. 1996a). Finally, we identify a C IV system at $z=2.014$ that shows a very narrow feature in Si IV and C IV absorption. The corresponding $b$ values (5.5 \kms and 8.9 \kms for Si IV and C IV) for this component suggest a temperature of $4.7 \sci{4} \rm K$. Because collisional ionization can explain the observed abundances only for $T > 8 \sci{4} \rm K$, we contend these ions must have formed through a different physical process (e.g. photoionization).