Photometric metallicity map of the Small Magellanic Cloud

TL;DR

This study presents the first detailed metallicity map of the Small Magellanic Cloud using photometric data, revealing a shallow metallicity gradient within its inner regions.

Contribution

It introduces a novel photometric method to map metallicity across the SMC, calibrating RGB slope to metallicity using spectroscopic data.

Findings

Average metallicity of SMC is around -0.94 dex.

Detected a shallow metallicity gradient within 2.5 degrees.

First metallicity map of SMC up to this radius.

Abstract

We have created an estimated metallicity map of the Small Magellanic Cloud (SMC) using the Magellanic Cloud Photometric Survey (MCPS) and Optical Gravitational Lensing Experiment (OGLE III) photometric data. This is a first of its kind map of metallicity up to a radius of $\sim$ 2.5$^{\circ}$. We identify the RGB in the V, (V$-$I) colour magnitude diagrams of small subregions of varying sizes in both data sets. We use the slope of the RGB as an indicator of the average metallicity of a subregion, and calibrate the RGB slope to metallicity using available spectroscopic data for selected subregions. The average metallicity of the SMC is found to be [Fe/H] = $-$0.94 dex ($\sigma$[Fe/H] = 0.09) from OGLE III, and [Fe/H] = $-$0.95 dex ($\sigma$[Fe/H] = 0.08) from MCPS. We confirm a shallow but significant metallicity gradient within the inner SMC up to a radius of 2.5$^{\circ}$ ($-$0.045$\pm$0.004 dex deg$^{-1}$ to $-$0.067$\pm$0.006 dex deg$^{-1}$).