The impact of supernova-driven winds on stream-fed protogalaxies

Abstract

Supernova (SN) driven winds are widely thought to be very influential in the high-redshift Universe, shaping the properties of the circumgalactic medium, enriching the intergalactic medium with metals and driving the evolution of low-mass galaxies. However, it is not yet fully understood how SN-driven winds interact with their surroundings in a cosmological context, nor is it clear whether they are able to significantly impact the evolution of low-mass galaxies from which they originate by altering the amount of the cold material these accrete from the cosmic web. Indeed, due to the strong constraints on resolution imposed by limited computational power, all cosmological hydrodynamic simulations to date resort to implementing more or less physically well motivated and complex subgrid models to trigger galactic winds. To explore this issue, we implement a standard Taylor–Sedov type solution, widely used in the community to depict the combined action of many SN explosions, in a cosmological resimulation of a low-mass galaxy at z≥ 9 from the ‘nut’ suite. However, in contrast with previous work, we achieve a resolution high enough to capture individual SN remnants in the Taylor–Sedov phase, for which the Taylor–Sedov solution actually provides an accurate description of the expansion. We report the development of a high-velocity, far-reaching galactic wind produced by the combined action of SNe in the main galaxy and its satellites, which are located in the same or a neighbouring dark matter halo. Despite this, we find that (i) this wind carries out very little mass (the measured outflow is of the order of a tenth of the inflow/star formation rate); and (ii) the cold gas inflow rate remains essentially unchanged from the run without SN feedback. Moreover, there are epochs during which star formation is enhanced in the feedback run relative to its radiative-cooling-only counterpart. We attribute this ‘positive’ feedback to the metal enrichment that is present only in the former. We conclude that at very high redshift, efficient SN feedback can drive large-scale galactic winds but does not prevent massive cold gas inflow from fuelling galaxies, resulting in long-lived episodes of intense star formation.