17 research outputs found
Atomic data for S II - Toward Better Diagnostics of Chemical Evolution in High-redshift Galaxies
Absorption-line spectroscopy is a powerful tool used to estimate element
abundances in the nearby as well as distant universe. The accuracy of the
abundances thus derived is, naturally, limited by the accuracy of the atomic
data assumed for the spectral lines. We have recently started a project to
perform the new extensive atomic data calculations used for optical/UV spectral
lines in the plasma modeling code Cloudy using state-of-the-art quantal
calculations. Here we demonstrate our approach by focussing on S II, an ion
used to estimate metallicities for Milky Way interstellar clouds as well as
distant damped Lyman-alpha (DLA) and sub-DLA absorber galaxies detected in the
spectra of quasars and gamma-ray bursts (GRBs). We report new extensive
calculations of a large number of energy levels of S II, and the line strengths
of the resulting radiative transitions. Our calculations are based on the
configuration interaction approach within a numerical Hartree-Fock framework,
and utilize both non-ralativistic and quasirelativistic one-electron radial
orbitals. The results of these new atomic calculations are then incorporated
into Cloudy and applied to a lab plasma, and a typical DLA, for illustrative
purposes. The new results imply relatively modest changes (~0.04 dex) to the
metallicities estimated from S II in past studies. These results will be
readily applicable to other studies of S II in the Milky Way and other
galaxies.Comment: Accepted for publication in The Astrophysical Journal; 34 pages, 10
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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.Comment: accepted The Astrophysical Journa
Atomic Data Revisions for Transitions Relevant to Observations of Interstellar, Circumgalactic, and Intergalactic Matter
Measurements of element abundances in galaxies from astrophysical spectroscopy depend sensitively on the atomic data used. With the goal of making the latest atomic data accessible to the community, we present a compilation of selected atomic data for resonant absorption lines at wavelengths longward of 911.753 Å (the H I Lyman limit), for key heavy elements (heavier than atomic number 5) of astrophysical interest. In particular, we focus on the transitions of those ions that have been observed in the Milky Way interstellar medium (ISM), the circumgalactic medium (CGM) of the Milky Way and/or other galaxies, and the intergalactic medium (IGM). We provide wavelengths, oscillator strengths, associated accuracy grades, and references to the oscillator strength determinations. We also attempt to compare and assess the recent oscillator strength determinations. For about 22% of the lines that have updated oscillator strength values, the differences between the former values and the updated ones are ≳ 0.1 dex. Our compilation will be a useful resource for absorption line studies of the ISM, as well as studies of the CGM and IGM traced by sight lines to quasars and gamma-ray bursts. Studies (including those enabled by future generations of extremely large telescopes) of absorption by galaxies against the light of background galaxies will also benefit from our compilation
Atomic Data for Zn ÉŞÉŞ: Improving Spectral Diagnostics of Chemical Evolution in High-Redshift Galaxies
Damped Lyα (DLA) and sub-DLA absorbers in quasar spectra provide the most sensitive tools for measuring the element abundances of distant galaxies. The 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 and UV spectral lines using state-of-the-art computer codes employing a very broad configuration interaction (CI) basis. Here we report our results for Zn ii, an ion used widely in studies of the interstellar medium (ISM) as well as DLAs and 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 CI approach within a numerical Hartree–Fock framework. We use both nonrelativistic 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 2026, 2062 oscillator strengths are higher than previous values by 0.10 dex. The Cloudy calculations for representative absorbers with the revised Zn atomic data imply ionization corrections lower than calculated earlier by 0.05 dex. The new results imply that 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
Radiative rates for transitions in Fe XVII
Energies of the lowest 157Â levels belonging to the (1s2) 2s22p6, 2s22p53, 2s22p54, 2s22p55,
2s2p63, 2s2p64 and 2s2p65 configurations of Fe XVII have been calculated using the GRASP
code of Dyall et al. ([CITE]). Additionally, radiative rates, oscillator strengths, and line strengths are calculated for all electric dipole (E1), magnetic dipole (M1),
electric quadrupole (E2), and magnetic quadrupole (M2) transitions among these levels. Comparisons are made with the results already available in the literature, and
the accuracy of the data is assessed. Our energy levels are expected to be accurate to better than 1%, whereas results for other parameters are probably accurate to
better than 20%
Energy levels and radiative rates for transitions in Cr-like Kr XIII, Tc XX and Xe XXXI.
Radiative rates, collision strengths and effective collision strengths for transitions in Gd XXXVII
Inner-shell photoexcitation of Fe XV and Fe XVI
The configuration-interaction method as implemented in the computer code CIV3 is used to determine energy levels, electric dipole radiative transition wavelengths, oscillator strengths and transition probabilities for inner-shell excitation of transitions in Fe XV and Fe XVI. Specifically, transitions are considered of the type 1s22s22p63s2–1s22s22p53l3l′3l′′ (l, l′ and l′′= s, p or d) in Fe XV and 1s22s22p63s–1s22s22p53l3l′ (l and l′= s, p or d) in Fe XVI, using the relativistic Breit-Pauli approach. An assessment of the accuracy of the derived atomic data is performed