The 2MASS Color-Magnitude Diagram of the Center of the Sagittarius Dwarf Galaxy: Photometric Measurements of a Surprisingly High Mean Metallicity

We present the Two Micron All Sky Survey (2MASS) (J-K, K) color-magnitude diagram for the region within 1° of the center of the Sagittarius dwarf spheroidal galaxy. Using the slope of the red giant branch (RGB), we determine a mean metallicity for the main stellar population of [Fe/H] = -0.5 ± 0.2. The Sagittarius RGB possesses a blue tail that overlaps with the foreground Milky Way giant branch and suggests that approximately one-third of the RGB is more metal-poor than [Fe/H] ∼ -1. Direct comparison with the Large Magellanic Cloud confirms the metal-rich nature of the bulk of the Sagittarius population. Our result is marginally consistent with the even higher metallicities determined from high-resolution spectroscopy.