arXiv:1011.2632

John H. Wise – Princeton University

Matthew J. Turk, Michael L. Norman – UC - San Diego

Tom Abel – Stanford University / KIPAC

Abstract

Population III stars first form in dark matter halos with masses around 106 Msun. By definition, they are metal-free, and their protostellar collapse is driven by molecular hydrogen cooling in the gas-phase, leading to a massive characteristic mass ~100 Msun and suppressed fragmentation. Population II stars with lower characteristic masses form when the star-forming gas reaches a critical metallicity of 10-6 - 10-3.5 Zsun, depending on whether dust cooling is important. We present adaptive mesh refinement radiation hydrodynamics simulations that follows the transition from Population III to II star formation. We model stellar radiative feedback with adaptive ray tracing. A top-heavy initial mass function for the Population III stars is considered, resulting in a plausible distribution of pair-instability supernovae and associated metal enrichment. We find that the gas fraction recovers from 5 percent to nearly the cosmic fraction in halos with merger histories rich in halos above 107 Msun. A single pair-instability supernova is sufficient to enrich the host halo to a metallicity floor of 10-3 Zsun and to transition to Population II star formation. This provides a natural explanation for the observed floor on damped Lyman alpha (DLA) systems metallicities reported in the literature, which is of this order. We find that stellar metallicities do not necessarily trace stellar ages, as mergers of halos with established stellar populations can create superpositions of t-Z evolutionary tracks. A bimodal metallicity distribution is created after a starburst occurs when the halo can cool efficiently through atomic line cooling.

Movies

High Resolution Images

Contact: John Wise (jwise {at} astro {dot} princeton [dot] edu

Figure 2: Density-weighted projections of gas density (top), temperature (middle), and metallicity (bottom) at z = 7.  The left column shows the entire simulation volume, where the center and right columns focus on the intense and quiet halos, which are marked by left and right arrows in the upper-left panel. The metallicity projections are a composite picture of metals originating from Pop III (red) and Pop II (blue) stars with magenta indicating a mixture of the two.

Projections

1. •Full box: Density, Temperature, Metallicity (Pop II), Metallicity (Pop III)
   

1. •Intense halo: Density, Temperature, Metallicity (Pop II), Metallicity (Pop III)
   

1. •Quiet halo: Density, Temperature, Metallicity (Pop II), Metallicity (Pop III)