A Keck HIRES Investigation of the Metal Abundances and Kinematics of Three Damped Lyα Systems toward Q2206−199

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 Lyα systems found at z = 1.920 and z = 2.076. For the z = 1.920 system, we measure accurate abundances (relative to solar) for Fe, Cr Si, Ni, Ti, and Zn: [Fe/H] = −0.705 ± 0.097, [Cr/H] = −0.580 ± 0.100, [Si/H] = −0.402 ± 0.098, [Ni/H] = −1.012 ± 0.095, [Ti/H] = −0.776 ± 0.081, and [Zn/H] = −0.379 ± 0.097. This system exhibits the highest metallicity we have measured for a damped Lyα system. By contrast the z = 2.076 system is the most metal poor ([Zn/H] < −1.745) we have analyzed, showing absorption features for only the strongest transitions. We determine accurate abundances for Fe, Si and Al: [Fe/H] = −2.621 ± 0.071, [Si/H] = −2.225 ± 0.075, and [Al/H] = −2.727 ± 0.070. Analyses of the abundance variations of Fe, Ni, Cr, and Si relative to Zn and the abundance trends versus condensation temperature do not offer positive evidence for the presence of dust in the damped system at z = 1.920. In addition, the relative abundance ratio [Ti/Fe] ≈ 0 further suggests the absence of ISM-like dust. Unfortunately, the lack of measurable Zn absorption in the z = 2.076 system does not allow a similar investigation for the presence of dust. In addition to the significant difference in metallicity, the two damped systems have vastly different kinematic characteristics. The z = 1.920 system spans ≈ 150 km s −1 in velocity space (measured from the low-ion transitions) while the z = 2.076 system spans a mere 30 km s −1. Furthermore, the z = 1.920 profiles are significantly asymmetric while the z = 2.076 profiles are 1 Visiting Astronomer, W.M. Keck Telescope. The Keck Observatory is a joint facility of the University