HE 0515-4414 - an unusual sub-damped Ly alpha system revisited

TL;DR

This study investigates the complex ionization, metallicity, dust depletion, and physical conditions of an unusual sub-damped Ly alpha system at z=1.15, revealing diverse ionization states and elemental abundances with implications for future DLA research.

Contribution

It provides a detailed analysis of ionization, dust depletion, and metallicity in a unique sub-DLA, highlighting the importance of considering ionization and depletion effects in such systems.

Findings

The velocity span of metal lines extends over 700 km/s.

The main absorber shows near-solar metallicity with varied dust depletion patterns.

Ionization effects can mimic alpha-element enrichment, affecting abundance interpretations.

Abstract

Using STIS and VLT UVES observations we have examined the ionization, abundances, and differential dust depletion of metals, the kinematic structure, and the physical conditions in the molecular hydrogen-bearing sub-damped Ly alpha system toward HE 0515-4414 at z = 1.15. The velocity interval of associated metal lines extends for 700 km/s. In addition, saturated H I absorption is detected in the blue damping wing of the main component. The column density ratios of associated Al II, Al III, and Fe II lines indicate that the absorbing material is ionized. 19 of in total 31 detected metal line components are formed within peripheral H II regions, while only 12 components are associated with the predominantly neutral main absorber. For the main absorber the observed abundance ratios of refractory elements to Zn range from Galactic warm disk [Si/Zn] = - 0.40, [Fe/Zn] = -1.10 to halo-like and essentially undepleted patterns. The dust-corrected metal abundances indicate a nucleosynthetic odd-even effect and might imply an anomalous depletion of Si relative to Fe for two components, but otherwise do correspond to solar ratios. The intrinsic average metallicity is almost solar [Fe/H] = -0.08, whereas the uncorrected average is [Zn/H] = -0.38. The ion abundances in the periphery conform with solar element composition. The detection of H II as well as the large variation in dust depletion for this sight line raises the question whether in future studies of damped Ly alpha systems ionization and depletion effects have to be considered in further detail. Ionization effects, for instance, may pretend an enrichment of alpha elements. An empirical recipe for detecting H II regions is provided.