Growing galaxies via superbubble-driven accretion flows

We use a suite of cooling halo simulations to study a new mechanism for rapid accretion of hot halo gas on to star-forming galaxies. Correlated supernova (SN) events create converging 'superbubbles' in the halo gas. Where these collide, the density increases, driving cooling filaments of low-metallicity gas that feed the disc. At our current numerical resolution (similar to 20 pc; m(gas) = 4 x 10(4) M-circle dot) we are only able to resolve the most dramatic events; however, as we increase the numerical resolution, we find that the filaments persist for longer, driving continued late-time star formation. This suggests that SN-driven accretion could act as an efficient mechanism for extracting cold gas from the hot halo, driving late-time star formation in disc galaxies. We show that such filament feeding leads to a peak star formation rate of similar to 3 M-circle dot yr(-1), consistent with estimates for the Milky Way (MW). The filaments we resolve extend to similar to 50 kpc, reaching column densities of N similar to 10(18) cm(-2). We show that such structures can plausibly explain the broad dispersion in Mg II absorption seen along sightlines to quasars. Our results suggest a dual role for stellar feedback in galaxy formation, suppressing hot-mode accretion while promoting cold-mode accretion along filaments. Finally, since the filamentary gas has higher angular momentum than that coming from hot-mode accretion, we show that this leads to the formation of substantially larger gas discs.