Study on the Abundance Discrepancy Problem in the Magellanic Clouds

TL;DR

This study measures chemical abundances of carbon and oxygen in the Magellanic Clouds' HII regions to investigate the abundance discrepancy problem and chemical evolution, using high-quality spectroscopic data from the VLT.

Contribution

It provides new measurements of C and O abundances from recombination lines, compares abundance discrepancy factors across galaxies, and explores chemical evolution through abundance gradients.

Findings

Detected faint recombination lines for CII and OII.

Compared abundance discrepancy factors with other galaxies.

Analyzed chemical evolution via radial abundance gradients.

Abstract

We present chemical abundances of carbon (C) and oxygen (O) in the Large and Small Magellanic Clouds from deep and high-quality optical spectra of HII regions. The data have been taken using the Ultraviolet-Visual Echelle Spectrograph at the 8.2-m Very Large Telescope with the goal of detecting the faint CII and OII recombination lines. For all the objects of the sample, we determine C^2+ abundances from recombination lines and O^2+ abundances from recombination lines and collisionally excited lines. In addition, we calculate the abundance discrepancy factors (ADFs) for O^2+ and C^2+, as well as the O/H, C/H and C/O ratios. We study the behaviour of the ADF comparing the values obtained in the Magellanic Clouds with those obtained for other HII regions in different galaxies. We also compare the nebular and stellar abundances in two regions of the sample. Finally, we discuss the chemical evolution of the MCs through the O/H, C/H and C/O radial gradients and the changes of the C/O ratio as a function of O/H.