Atomic data for Zn II - Improving Spectral Diagnostics of Chemical Evolution in High-redshift Galaxies

TL;DR

This paper provides new atomic data for Zn II, improving the accuracy of spectral diagnostics used to measure chemical abundances in high-redshift galaxies, which affects metallicity estimates in DLA and sub-DLA systems.

Contribution

The study presents updated atomic parameters for Zn II using advanced computational methods, enhancing the precision of abundance measurements in astrophysical environments.

Findings

New oscillator strengths for Zn II lines are 0.10 dex higher than previous values.

Ionization corrections for Zn are reduced by 0.05 dex with new data.

Zinc metallicities in DLAs and sub-DLAs are revised downward by 0.1 to 0.15 dex.

Abstract

Damped Lyman-alpha (DLA) and sub-DLA absorbers in quasar spectra provide the most sensitive tools for measuring element abundances of distant galaxies. Estimation of abundances from absorption lines depends sensitively on the accuracy of the atomic data used. We have started a project to produce new atomic spectroscopic parameters for optical/UV spectral lines using state-of-the-art computer codes employing very broad configuration interaction basis. Here we report our results for Zn II, an ion used widely in studies of the interstellar medium (ISM) as well as DLA/sub-DLAs. We report new calculations of many energy levels of Zn II, and the line strengths of the resulting radiative transitions. Our calculations use the configuration interaction approach within a numerical Hartree-Fock framework. We use both non-relativistic and quasi-relativistic one-electron radial orbitals. We have incorporated the results of these atomic calculations into the plasma simulation code Cloudy, and applied them to a lab plasma and examples of a DLA and a sub-DLA. Our values of the Zn II {\lambda}{\lambda} 2026, 2062 oscillator strengths are higher than previous values by 0.10 dex. Cloudy calculations for representative absorbers with the revised Zn atomic data imply ionization corrections lower than calculated before by 0.05 dex. The new results imply Zn metallicities should be lower by 0.1 dex for DLAs and by 0.13-0.15 dex for sub-DLAs than in past studies. Our results can be applied to other studies of Zn II in the Galactic and extragalactic ISM.