Mass, Metal, and Energy Feedback in Cosmological Simulations

Abstract

Using Gadget-2 cosmological hydrodynamic simulations including an observationally-constrained model for galactic outflows, we investigate how feedback from star formation distributes mass, metals, and energy on cosmic scales from z=6->0. We include instantaneous enrichment from Type II SNe, delayed enrichment from Type Ia SNe and stellar (AGB) mass loss, and we individually track C, O, Si, and Fe. Following on the successes of the momentum-driven wind scalings, we improve our implementation with an on-the-fly galaxy finder to derive wind properties based on host galaxy masses. By tracking wind particles in a suite of simulations, we find: (1) Wind material reaccretes onto a galaxy on a recycling timescale that varies inversely with galaxy mass. Hence metals driven into the IGM by galactic superwinds cannot be assumed to leave their galaxy forever. Wind material is typically recycled several times; the median number of ejections for a given wind particle is 3, so by z=0 the total mass ejected in winds exceeds 0.5\Omega_b. (2) The physical distance winds travel is fairly independent of redshift and galaxy mass (60-100 physical kpc). For sizable galaxies at later epochs, winds typically do not escape the galaxy halo, and rain back down in a halo fountain. High-z galaxies enrich a significantly larger comoving volume of the IGM, with metals migrating back into galaxies to lower z. (3) The energy imparted into winds scales with M_{gal}^{1/3}, and energy from another source besides SNe (such as photons from young stars) may be required to distributed cosmic metals as observed. (4) The production of all 4 metals tracked is globally dominated by Type II SNe at all epochs. However, intracluster gas iron content triples as a result of non-Type II sources, and the low-z IGM carbon content is boosted by AGB feedback.