Improved Ni II oscillator strengths from quasar absorption systems

Abstract

Aims. We wish to improve the accuracy of oscillator strength values for several Ni ii UV transitions and measure for the first time the f -value of a few other weak transitions for which no laboratory nor astronomical measurement is presently available. Methods. Four quasars displaying five damped Lyman α systems with relatively strong Ni ii lines were selected. From the analysis of the excellent high resolution spectra available, we determined the relative f -value of Ni ii transitions by comparing the strength of the corresponding absorption profiles. To quantify the latter, we used the apparent optical depth method for resolved features, equivalent width measurements for optically thin lines and line fitting with VPFIT. Absolute f -values were then derived by relating our determinations to the available laboratory measurements.Results. Thanks to the good signal-to-noise ratio of the spectra and to the suitable properties of the absorption systems investigated, we are able to significantly improve the determination of the f -value for 13 Ni ii transitions falling in the 1317-1804 Å interval. Our results are found to be consistent with other earlier determinations for ten of these transitions; our median relative accuracy for these f -values is 6.5%. For three weak transitions near 1502, 1773, and 1804 Å, which have not been detected previously in astronomical spectra, we can get a first measurement of their f -value. Conclusions. Our work illustrates that, thanks to the redshift and the absence of variations of physical constants on cosmological scales, the analysis of absorption lines induced by remote gas in quasar spectra can nowadays provide valuable constraints on atomic data in the UV range.

Dust depletion of metals from local to distant galaxies

“…We homogenize by correcting the column densities to the newest possible oscillator strengths for all the samples. We adopted the oscillator strengths from Cashman et al (2017) for Kr i, Mg ii, Si ii, Cu ii, Co ii, Mn ii, Cr ii, Al ii and Ti ii, from Boissé & Bergeron (2019) for Ni ii, from Kisielius et al (2015) for Zn ii, from Kisielius et al (2014) for S ii and from Kurucz (2017) for P. For the other metals, if there is no recent change to the oscillator strength, the value from Morton (2003) is used.…”

“…Due to the high column density of neutral hydrogen in QSO-DLAs, which shields metals against higher ionizations, no ionization corrections are needed to derive the metal abundances. We adopted the newest oscillator strengths from Cashman et al (2017) for Ti ii, from Boissé & Bergeron (2019) for Ni ii and from Kisielius et al (2015) for Zn ii. For Fe ii there is no recent change to the oscillator strength, so the value from Morton (2003) is used.…”

A High-precision Survey of the D/H Ratio in the Nearby Interstellar Medium

“…The f-values for some of the Ni II transitions shown in Table A1 were slightly changed after the Ni column densities were computed for this sight line (Boissé & Bergeron 2019). To be conservative, we have made a corresponding correction to these column densities on the order of 0.06 dex per component, and increased the errors by 0.03 dex per component and 0.09 dex in the sum.…”

The Distribution of Metallicities in the Local Galactic Interstellar Medium

“…New experimental f -values are now available for commonly observed transitions of P ii (Federman et al 2007;Brown et al 2018) (Heidarian et al 2015). In addition, empirically-derived f -values have been determined for several transitions of Fe ii (Miller et al 2007) and Ni ii (Jenkins & Tripp 2006;Boissé & Bergeron 2019). There are no experimentally-determined f -values for the Mn ii λλ1197, 1199, 1201 triplet.…”