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

A correlation between the metallicity, [M/H], and rest-frame MgII equivalent width, Wλ2796r, is found from 49 damped Lyα absorbers (DLAs) and strong sub-DLAs drawn from the literature over the redshift range 0.2 < zabs < 2.6. The correlation is significant at 4.2σ and improves to 4.7σ 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 Wλ2796r > 0.7Å, the correlation remains at >3σ significance. Since the MgII λ2796 transition is predominantly saturated in DLAs (which always have Wλ2796r greater than 0.3Å), Wλ2796r 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]-Wλ2796r 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 H2 absorbers have very high Wλ2796r and very broad velocity structures which show characteristics usually associated with outflows. Follow-up ultraviolet- and blue-sensitive high-resolution spectra of high-Wλ2796r systems, initially identified in low-resolution spectra, may therefore yield a large number of new H2 discoveries.