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

Abstract

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 Lyα 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 logN(HI)< 21.0 show lower [S/H] and [Fe/H] (relative to intervening systems with similar redshift and N(Hi)), whilst higher [S/H] and [Si/H] are seen in PDLAs with logN(HI)> 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 (v 90 ). 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 metalpoor DLA with [Fe/H]= −2.82 (the third lowest [Fe/H] in DLAs identified to date) at z abs = 4.25. Lastly we study the dust-corrected [Zn/Fe], emphasizing that near-IR coverage of X-Shooter provides unprecedented access to Mgii, Caii and Tiii lines (at redshifts 3-4) to provide additional evidence for subsolar [Zn/Fe] ratio in DLAs.

The comoving mass density of Mg ii from z ∼ 2 to 5.5

“…MS13 find that at the mean redshift of their sample (<z> 3.402) the ratio of Mg ii absorbers that are DLAs is ∼40.7% which is up from 16.7% at <z>=0.927. Berg et al (2016) also find that the ratio of DLAs associated with Mg ii systems with W 2796 ≤0.6Å increases by a factor of 5 from z ∼1 to z ∼4. These findings suggest that, with increasing redshift, Mg ii systems with W 2796 ≤0.6Å become even more important in tracking cool neutral gas.…”

“…It has an ionisation energy of 1.1 Ryd and has been established as a tracer of H i in the redshift range 0.5≤z≤1.4 (Ménard & Chelouche 2009). Furthermore, both MS13 and Berg et al (2016) find that the fraction of Mg ii absorbers associated with DLAs increases with redshift. MS13 find that at the mean redshift of their sample (<z> 3.402) the ratio of Mg ii absorbers that are DLAs is ∼40.7% which is up from 16.7% at <z>=0.927.…”

Sub-damped Lyman α systems in the XQ-100 survey – I. Identification and contribution to the cosmological H i budget

“…For consistency with Sánchez-Ramírez et al (2016), we restricted the XQ-100 sample to exclude systems with an absorption redshift within 5000 km s −1 of the QSO emission redshift. These proximate systems likely trace a different population of systems compared to their intervening counterparts, (Ellison et al 2002(Ellison et al , 2010Berg et al 2016;Perrotta et al 2016) and are typically ignored when computing Ω Hi . To properly measure f (N, X) for DLAs, a sample size much larger than the 33 DLAs identified in the XQ-100 sample must be used in order to statistically probe the high column density end of f (N, X) (logN(Hi)> 21.5).…”

“…The XQ-100 Legacy Survey (PI S. López) observed 100 QSO sightlines at redshift zem∼ 3.5-4.5 with the X-Shooter Spectrograph (Vernet et al 2011) on the Very Large Telescope (VLT) in Chile. The QSOs were purposefully chosen to be blind to any intervening absorption line systems, thus providing a random sample of sub-DLAs and DLAs to study the cosmological implications of these intervening absorbers (Sánchez-Ramírez et al 2016;Berg et al 2016Berg et al , 2017Christensen et al 2017). For more details about the XQ-100 science cases and survey design, see López et al (2016).…”

“…where zmin and zmax are the minimum and maximum redshift observed along the QSO path, while ΩM and ΩΛ are the matter and dark energy densities of the Universe observed at the current epoch. zmin is set by the Lyman limit of the QSO, while zmax is set as zem −5000 km s −1 to remove proximate systems that can be associated with the QSO (Ellison et al 2002(Ellison et al , 2010Berg et al 2016;Perrotta et al 2016). Rather than using the standard bins of column density, which can hide or amplify features depending on the choice of bins, we elected to use a sliding logN(Hi) bin to quantify the median f (N, X) in each column density bin.…”