Elemental depletions in the Magellanic Clouds and the evolution of depletions with metallicity

TL;DR

This study analyzes gas and dust composition in the Magellanic Clouds using UV absorption spectroscopy, revealing how depletions vary with metallicity and indicating dust processing in different galactic environments.

Contribution

It provides new measurements of element depletions in the Magellanic Clouds and compares them across different metallicities, highlighting variations in dust-to-gas ratios and depletion patterns.

Findings

P and Zn are not reliable metallicity indicators at and above SMC metallicity.

Depletions of Si, Cr, and Fe are lower in the SMC compared to MW and LMC.

Gas-to-dust ratios vary within galaxies, indicating dust destruction and growth processes.

Abstract

We present a study of the composition of gas and dust in the Large and Small Magellanic Clouds (LMC and SMC, together -- the MCs) as measured by UV absorption spectroscopy. We have measured P II and Fe II along 85 sightlines toward the MCs using archival FUSE observations. For 16 of those sightlines, we have measured Si II, Cr II, and Zn II from new HST COS observations. We have combined these measurements with H I and H$_2$ column densities and reference stellar abundances from the literature to derive gas-phase abundances, depletions, and gas-to-dust ratios (GDRs). 80 of our 84 P measurements and 13 of our 16 Zn measurements are depleted by more than 0.1 decades, suggesting that P and Zn abundances are not accurate metallicity indicators at and above the metallicity of the SMC. The maximum P and Zn depletions are the same in the MW, LMC, and SMC. Si, Cr, and Fe are systematically less depleted in the SMC than in the MW or LMC. The minimum Si depletion in the SMC is consistent with zero. Our depletion-derived GDRs broadly agree with GDRs from the literature. The GDR varies from location to location within a galaxy by a factor of up to 2 in the LMC and up to 5 in the SMC. This variation is evidence of dust destruction and/or growth in the diffuse neutral phase of the interstellar medium.