J/MNRAS/436/413   VISTA Sgr dSph ZJKs photometry               (McDonald+, 2013)
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Beginning of ReadMe : J/MNRAS/436/413 VISTA ZJKs photometry of Sgr dSph (McDonald+, 2013) ================================================================================ VISTA's view of the Sagittarius dwarf spheroidal galaxy and southern Galactic bulge. McDonald I., Zijlstra A.A., Sloan G.C., Kerins E.J., Lagadec E., Minniti D., Santucho M.V., Gurovich S., Dominguez Romero M.J.L. <Mon. Not. R. Astron. Soc., 436, 413-429 (2013)> =2013MNRAS.436..413M ================================================================================ ADC_Keywords: Galaxies, nearby ; Milky Way ; Photometry, infrared Keywords: stars: AGB and post-AGB - stars: evolution - stars: fundamental parameters - stars: late type - Galaxy: bulge - galaxies: individual: Sgr dSph Abstract: We present the deepest near-infrared (ZJKs) photometry yet obtained of the Sagittarius dwarf spheroidal (Sgr dSph), using Visible and Infrared Survey Telescope for Astronomy (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] -1dex 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 galaxy can be well approximated by a roughly ovaloid projection of characteristic size 4degx2deg, beyond which the projected stellar density is less than half that of the region surrounding the core. The galaxy's major axis is perpendicular to the Galactic Plane, as in previous studies. We find slight evidence to confirm a metallicity gradient in the Sgr dSph and use isochrones to fit a distance of 24.3+/-2.3kpc. We were unable to fully constrain the metallicity distribution of the Sgr dSph due to the Bulge contamination and strong correlation of [alpha/Fe] with metallicity; however, we find that metal-poor stars ([Fe/H]< -1) make up < 29% of the Sgr dSph's upper red giant branch population. The Bulge population is best fitted by a younger population with [Fe/H] approx 0 and [alpha/Fe] approx 0 or slightly higher. We find no evidence for a split, peanut- or X-shaped Bulge population in this line of sight (l=5.6+/- 1deg, b=-14.1+/- 3deg). Description: The VISTA Infrared Camera (VIRCAM) surveyed the core of the Sgr dSph over 16 nights between 2012 April 06 and 2012 June 07. VIRCAM consists of 16 imaging chips which create a pawprint that must be moved around the sky to create a contiguous imaging tile of around 1.5 square degrees. The simultaneous ZJKs-band images allowed for a relatively simple merging procedure. Objects identified in different filters were simply grouped by finding the nearest J- and Ks-band neighbour to each Z-band detection.