VISTA's view of the Sagittarius dwarf spheroidal galaxy and southern Galactic Bulge
Iain McDonald, Albert A. Zijlstra, Gregory C. Sloan, Eamonn J. Kerins,, Eric Lagadec, Dante Minniti, M. Victoria Santucho, Sebastiano Gurovich,, Mariano J. de L. Dominguez Romero

TL;DR
This study provides deep near-infrared photometry of the Sagittarius dwarf galaxy and Galactic Bulge, revealing stellar populations, structure, and metallicity gradients, while addressing contamination challenges and mapping the galaxy's extent.
Contribution
First near-infrared detection of the Sagittarius dwarf's horizontal branch and detailed mapping of its stellar density and metallicity gradients.
Findings
Sagittarius dwarf is roughly oval, 4x2 degrees in size
Metal-poor stars constitute less than 29% of the upper RGB
No evidence found for split or X-shaped Bulge population
Abstract
We present the deepest near-infrared (ZJKs) photometry yet obtained of the Sagittarius dwarf spheroidal (Sgr dSph), using VISTA to survey 11 square degrees centred on its core. We list locations and ZJKs-band magnitudes for over 2.9 million sources in the field. We discuss the isolation of the Sgr dSph from the foreground and Galactic Bulge populations, identify the Sgr dSph's horizontal branch in the near-infrared for the first time, and map the density of the galaxy's stars. We present isochrones for the Sgr dSph and Bulge populations. These are consistent with the previously-reported properties of the Sgr dSph core: namely that it is dominated by a population between [Fe/H] ~ -1 dex and solar, with a significant [alpha/Fe] versus [Fe/H] gradient. While strong contamination from the Galactic Bulge prevents accurate measurement of the (Galactic) north side of the Sgr dSph, the dwarf…
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