Photometric metallicity map of the Small Magellanic Cloud

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 ∼2.5°. We identify the Red Giant Branch (RGB) in the V, (V − I) colour–magnitude diagrams of small sub-regions of varying sizes in both data sets. We use the slope of the RGB as an indicator of the average metallicity of a sub-region and calibrate the RGB slope to metallicity using available spectroscopic data for selected sub-regions. The average metallicity of the SMC is found to be [Fe/H] = −0.94 dex (σ[Fe/H] = 0.09) from OGLE III and [Fe/H] = −0.95 dex (σ[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° (−0.045 ± 0.004 to −0.067 ± 0.006 dex deg−1).