The Ultra-Diffuse Dwarf Galaxy Crater II

Crater II is the fourth largest galaxy among the satellites of the Milky Way, only surpassed by the Magellanic Clouds, Sagittarius and the recently discovered Antlia II galaxy. This galaxy lies in the frontier between classical satellites and ultra-faint dwarf galaxies. We explore the stellar population of Crater II through both its variable star population and a deep color-magnitude population. The large field of view of the Dark Energy Camera (DECam) at the 4m Blanco Telescope at Cerro Tololo Inter-American Observatory (CTIO), Chile, was the ideal instrument to observe this large galaxy. We identified 130 periodic variable stars, including RR Lyrae stars, anomalous Cepheids, SX Phoenicis stars, and eclipsing variables. The large number of RR Lyrae stars allowed us to obtain an accurate distance modulus, to explore the shape of the galaxy, and to asses the metallicity spread of the old population of Crater II. On the other hand, the deep CMD shows only old stars with a clearly bifurcated subgiant branch that feeds a narrow red giant branch.