The Seven Dwarfs: Formation and Evolution of Dwarf Galaxies in an Isolated Environment
I will present results from a suite of cosmological hydrodynamic simulations of a group of seven field dwarf galaxies. The properties of the simulated dwarfs are strongly modulated by the depth of the gravitational potential. For halos with masses below 1e9 Msun, photoionisation heating from the ultraviolet background prevents gas from forming stars. The more massive dwarfs galaxies have blue colors, low star formation efficiencies, high cold gas to stellar mass ratios (0.2 ≤ M_HI/M* ≤ 20), and low gaseous and stellar metallicities. Their bursty star formation histories are characterized by peak sSFR in excess of 50 − 100 Gyr−1, far outside the realm of normal galaxies. The median stellar age of the simulated galaxies decreases with decreasing halo mass, with the two lower mass dwarfs being predominantly young and lightened up by tidal interactions. Galactic outflows produce sub-solar effective yields and pollute a Mpc-size region of the IGM with metals, but are not sufficient to completely quench star formation. For the most massive systems in the simulation, baryonic process has a strong impact on the dark matter distribution at the halo centres. Repeated supernova-driven gas outflows remove dark matter (DM) cusps, and create kpc-size cores. I will discuss the energetics and the timetable of this cusp-core transformation.