The Role of Heating and Enrichment in Galaxy Formation

Abstract

We show that the winds identified with high-redshift low-mass galaxies may strongly affect the formation of stars in more massive galaxies that form later. With 3D realizations of a simple nonlinear growth model we track gas shocking, metal enrichment, and cooling, together with dark halo formation. We show that outflows typically strip baryonic material out of pre-virialized intermediate mass halos, suppressing star formation. More massive halos can trap the heated gas but collapse later, leading to a broad bimodal redshift distribution, with a larger characteristic mass and metallicity associated with the lower redshift peak. This scenario accounts for the observed bell-shaped luminosity function of early-type galaxies, explains the small number of Milky-Way satellite galaxies relative to standard Cold Dark Matter proscriptions, and provides a reasonable explanation for the lack of metal poor stars in the solar neighborhood and the more general lack of low-metallicity stars in other massive galaxies relative to “closed-box” models of chemical enrichment. Heating of the intergalactic medium by early outflows should produce spectral distortions in the cosmic microwave background that will be measurable with the next generation of experiments. Subject headings: galaxies: formation – galaxies: interactions– large-scale structure of the universe – galaxies: elliptical