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 ∼ 1/3 of the RGB is more metal-poor than [Fe/H] ~−1. Direct comparison to 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