The Puzzling Problems Of The Local Group Dwarf Spheroidals; The Fight For Survival In The Early Universe.

The dwarf spheroidal galaxies (dSphs) of our Local Group pose challenges to our theories of galaxy formation and evolution in a ΛCDM Universe. Despite the wealth of information available from these systems provided by their close proximity, little is understood about their individual histories. The faintest dSphs host a single, ancient stellar population, the formation of stars in these galaxies ceased billions of years ago and they are devoid of gas. As these systems are so small, they are susceptible to gas loss, however this cannot be a simple process due to the diverse range of properties they exhibit, despite residing in haloes of the same mass. In this thesis I address two processes resulting in gas removal at early times and attempt to further our understanding of these systems by isolating each process. I use hydrodynamical simulations to explore the impact of each process to asses their significance and to identify the dominant influences on their evolution. Firstly I simulate the effect of SNe feedback on dSph progenitors undergoing an initial burst of star formation at high redshift (z~10) and the conditions under which they retain gas. In order to host an extended burst of star formation the number of supernovae must be lower than that expected if we assume star formation proceeds in a similar fashion to that in larger galaxies. The impact of an AGN outflow originating from the Milky Way on the surrounding dwarf galaxies is also simulated, which easily strips gas from these systems, leaving behind a halo with an ancient stellar population. The difficulty of retaining gas in the early Universe could be alleviated if they accreted gas during the period of extended star formation. I investigate these three process in the context of isolated dwarfs