IAUS379: Dynamical Masses of Local Group Galaxies

Observational studies have identified several sub-structures in different regions of the Magellanic Clouds (MCs). One such interesting sub-structure in the Small Magellanic Cloud (SMC) is a dual population of intermediate-age giant stars which are spatially and kinematically distinct. Comparisons with simulations suggest that the foreground population might be tidally stripped from the SMC main-body, but their origin is not clearly proven yet. If we have homogeneous metallicity measurements of the sources from these sub-structures, we can see whether they are having similar values or different from the main-body population. Hence, metallicity measurements of these populations will help us understand their origin and/or their association with the Large Magellanic Cloud (LMC). However, spectroscopic metallicities are only available for a few thousand sources and also from different instruments at various spectral resolutions, which makes it difficult to compare their values and draw conclusions from the results. The third data release of Gaia has provided us with ~ 0.17 million XP spectra of the SMC sources as faint as ~ 18 mag in G-band which are spread across ~ 10° from the SMC center. Stromgren photometry is a well-established method to estimate the photometric metallicities. Gaia BP spectra covers the u, v, b and y Strömgren bands. Using the estimated Strömgren magnitudes from the Gaia BP spectra, we calibrated the [Fe/H] values. We compared a subset of the SMC sources that has [Fe/H] values from the high-resolution (~ 22,500) APOGEE spectrograph for the validation of our method. Using those metallicity measurements, we produce a homogeneous metallicity map of the entire SMC also with a higher spatial resolution and study the metallicity of different sub-structures to shed light on their possible origin and/or their associations with the LMC.