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