Outside-In Evolution with a Twist: Metallicity Gradients and Asymmetries in the SMC

TL;DR

This study analyzes metallicity distributions in the Small Magellanic Cloud using near-infrared calcium triplet lines, revealing gradients, asymmetries, and possible effects of tidal interactions with the LMC.

Contribution

It provides the first detection of a positive metallicity gradient within 1.2 degrees and links azimuthal asymmetries to tidal effects, advancing understanding of SMC evolution.

Findings

Median metallicity of [Fe/H]=-1.05 dex

Negative metallicity gradient of -0.064 dex/deg

Hints of positive gradient within 1.2 degrees

Abstract

Taking advantage of the near-infrared calcium triplet lines, we determine metallicities for a sample of more than 3,500 red giant stars in the field of the Small Magellanic Cloud (SMC). We find a median metallicity of [Fe/H]=-1.05$\pm$0.01 dex with a negative metallicity gradient of -0.064$\pm$0.007 dex deg$^{-1}$ between 1.2\deg~to 6.0\deg consistent with an outside-in evolution scenario. For the first time, we detect hints of a positive metallicity gradient within 1.2\deg, likely reflecting radial migration or centralised chemical enrichment. Azimuthal metallicity asymmetries are detected, with flatter gradients in the eastern and southern quadrants and steeper ones in the north and west. They are consistent with tidal interaction effects from the Large Magellanic Cloud (LMC). Finally, in spite of a clear distance and velocity bifurcations in the east, they seem to share a common chemical origin, in agreement with other studies.