Investigating a possible connection between two ultra-faint Milky Way satellites: Pegasus III and Pisces II

The currently most favoured model for galaxy formation is the Cold Dark Matter + Cosmological Costant theory, which suggests a hierarchical assembly scenario. According to this model masses of larger galaxies form by merger and accretion of smaller structures. Ideal candidates to be the surviving `building blocks' of the assembly process are the dwarf spheroidal galaxies (dSphs) found around spirals like the Milky Way (MW) and the Andromeda galaxy (M31). However, the "classical" dSphs are much fewer in number than predicted by the theory (missing satellites problem). On the other hand, the "ultra-faint" dwarfs (UFDs), which are fainter than the "classical" dSphs and discovered in the last decade, have partially alleviated this problem. The MW and the M31 surroundings are ideal environments to search for and study these galaxies in order to understand their role within the galaxy formation context. The majority of the new MW satellites has been discovered in the last few years using data from the SDSS survey. The variable stars are powerful tools to explore the nature of the dSphs, as they are primary distance indicators and excellent stellar population tracers. The most common type of variable stars in the dSph galaxies are the RR Lyrae stars (RRL), which are old population tracers, and the Anomalous Cepheids (ACs), tracers of an intermediate age population. This work aimed at investigating whether there are signatures of a physical connection between the two UFD MW satellites, Pegasus III and Pisces II, which lie at similar distances from us and are spatially very close, and they also share similar properties. We focused on the derivation of ages, metallicities, distance moduli, definition of the Oosterhoff type and spatial distribution, using the variable stars and the color-magnitude diagrams of the resolved stellar populations. Results obtained for the two galaxies have been compared with each other and with those of other MW satellites.