The connection between metallicity and metal-line kinematics in (sub-)damped Lyα systems

A correlation between the metallicity, [M/H], and rest-frame Mg II equivalent width, W-r(lambda 2791), is found from 49 damped Ly alpha absorbers (DLAs) and strong sub-DLAs drawn from the literature over the redshift range 0.2 < Z(abs) < 2.6. The correlation is significant at 4.2 sigma and improves to 4.7 sigma when the mild evolution of [M/H] with redshift is taken into account. Even when including only the 26 DLAs (i.e. excluding sub-DLAs) which have Zn-metallicities and W-r(lambda 2796) > 0.7 angstrom, the correlation remains at > 3 sigma significance. Since the Mg II lambda 2796 transition is predominantly saturated in DLAs (which always have W-r(lambda 2796) greater than 0.3 angstrom), W-r(lambda 2796) is far more sensitive to the kinematic spread of the metal velocity components across the absorption profile than it is to [M/H]. Thus, the observed [M/H]-W-r(lambda 2796) correlation points to a strong link between the absorber metallicity and the mechanism for producing and dispersing the velocity components. We also note that approximately half of the 13 known H-2 absorbers have very high W-r(lambda 2796) and very broad velocity structures which show characteristics usually associated with outflows. Follow-up ultraviolet- and blue-sensitive high-resolution spectra of high- W-r(lambda 2796) systems, initially identified in low-resolution spectra, may therefore yield a large number of new H-2 discoveries.