Interstellar Ti II in the Milky Way and Magellanic Clouds

TL;DR

This study analyzes Ti II absorption lines in the Milky Way and Magellanic Clouds to understand interstellar depletion patterns and environmental differences, with implications for extragalactic and cosmological observations.

Contribution

It provides detailed high- and moderate-resolution spectroscopic data revealing differences in titanium depletion and ionization across different interstellar environments and galaxies.

Findings

Titanium depletion is less severe in the LMC and SMC than in the Milky Way.

Spectral profile comparisons show component-to-component differences in ionization and depletion.

Lower metallicity galaxies exhibit distinct depletion patterns affecting gas-phase abundance interpretations.

Abstract

We discuss several sets of Ti II absorption-line data, which probe a variety of interstellar environments in our Galaxy and in the Magellanic Clouds. Comparisons of high-resolution (FWHM ~ 1.3-1.5 km/s) Ti II spectra of Galactic targets with corresponding high-resolution spectra of Na I, K I, and Ca II reveal both similarities and differences in the detailed structure of the absorption-line profiles -- reflecting component-to-component differences in the ionization and depletion behaviour of those species. Moderate-resolution (FWHM ~ 3.4-4.5 km/s) spectra of more heavily reddened Galactic stars provide more extensive information on the titanium depletion in colder, denser clouds -- where more than 99.9 per cent of the Ti may be in the dust phase. Moderate-resolution (FWHM ~ 4.5-8.7 km/s) spectra of stars in the Magellanic Clouds suggest that the titanium depletion is generally much less severe in the LMC and SMC than in our Galaxy [for a given N(H_tot), E(B-V), or molecular fraction f(H_2)] -- providing additional evidence for differences in depletion patterns in those two lower-metallicity galaxies. We briefly discuss possible implications of these results for the interpretation of gas-phase abundances in QSO absorption-line systems and of variations in the D/H ratio in the local Galactic ISM.