Explosions during Galaxy Formation

As an idealized model of the effects of energy release by supernovae during galaxy formation, we consider an explosion at the center of a halo which forms at the intersection of filaments in the plane of a cosmological pancake by gravitational instability during pancake collapse. Such halos resemble the virialized objects found in N–body simulations in a CDM universe and, therefore, serve as a convenient, scale–free test–bed model for galaxy formation. ASPH/PM simulations reveal that such explosions are anisotropic. The energy and metals are channeled into the low density regions, away from the pancake plane. The pancake remains essentially undisturbed, even if the explosion is strong enough to blow away all the gas located inside the halo at the onset of the explosion and reheat the IGM surrounding the pancake. Infall quickly replenishes this ejected gas and gradually restores the gas fraction as the halo mass continues to grow. Estimates of the collapse epoch and SN energy–release for galaxies of different mass in the CDM model can relate these results to scale–dependent questions of blow–out and blow–away and their implication for early IGM heating and metal enrichment and the creation of dark–matter–dominated dwarf galaxies.