Chemical abundances of the damped Lyman α systems in the XQ-100 survey

The XQ-100 survey has provided high signal-noise spectra of 100 redshift 3–4.5 quasars with the X-Shooter spectrograph. The metal abundances for 13 elements in the 41 damped Ly α systems (DLAs) identified in the XQ-100 sample are presented, and an investigation into abundances of a variety of DLA classes is conducted. The XQ-100 DLA sample contains five DLAs within 5000 km s−1 of their host quasar (proximate DLAs; PDLAs) as well as three sightlines which contain two DLAs within 10 000 km s−1 of each other along the same line of sight (multiple DLAs; MDLAs). Combined with previous observations in the literature, we demonstrate that PDLAs with log N(H i) < 21.0 show lower [S/H] and [Fe/H] [relative to intervening systems with similar redshift and N(H i)], whilst higher [S/H] and [Si/H] are seen in PDLAs with log N(H i) > 21.0. These abundance discrepancies are independent of their line-of-sight velocity separation from the host quasar, and the velocity width of the metal lines (v90). Contrary to previous studies, MDLAs show no difference in [α/Fe] relative to single DLAs matched in metallicity and redshift. In addition, we present follow-up UVES data of J0034+1639, a sightline containing three DLAs, including a metal-poor DLA with [Fe/H] = −2.82 (the third lowest [Fe/H] in DLAs identified to date) at zabs = 4.25. Lastly we study the dust-corrected [Zn/Fe], emphasizing that near-IR coverage of X-Shooter provides unprecedented access to Mg ii, Ca ii and Ti ii lines (at redshifts 3–4) to provide additional evidence for subsolar [Zn/Fe] ratio in DLAs.