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

Abstract

A correlation between the metallicity, [M/H], and rest-frame Mg II equivalent width, Wrλ2796, 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 Wrλ2796 > 0.7 Å, the correlation remains at >3σ significance. Since the Mg II λ2796 transition is predominantly saturated in DLAs (which always have Wrλ2796 greater than 0.3 Å), Wrλ2796 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]-Wrλ2796 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 W rλ2796 and very broad velocity structures which show characteristics usually associated with outflows. Follow-up ultraviolet- and blue-sensitive high-resolution spectra of high-Wrλ2796 systems, initially identified in low-resolution spectra, may therefore yield a large number of new H2 discoveries. © 2007 RAS.