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Title:
The Fate of the First Galaxies. III. Properties of Primordial Dwarf Galaxies and Their Impact on the Intergalactic Medium
Authors:
Ricotti, Massimo; Gnedin, Nickolay Y.; Shull, J. Michael
Affiliation:
AA(Department of Astronomy, University of Maryland, College Park, MD 20742; .), AB(Particle Astrophysics Center, Fermi National Accelerator Laboratory, Batavia, IL 60510; .; Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL 60637.; Kavli Institute for Cosmological Physics, University of Chicago, Chicago, IL 60637.), AC(CASA, Department of Astrophysical and Planetary Sciences, University of Colorado, 389-UCB, Boulder, CO 80309; .)
Publication:
The Astrophysical Journal, Volume 685, Issue 1, pp. 21-39. (ApJ Homepage)
Publication Date:
09/2008
Origin:
UCP
ApJ Keywords:
Cosmology: Early Universe, Galaxies: Dwarf, Galaxies: Formation, Galaxies: Intergalactic Medium, Methods: Numerical
Abstract Copyright:
(c) 2008: The American Astronomical Society
DOI:
10.1086/590901
Bibliographic Code:
2008ApJ...685...21R

Abstract

In two previous papers, we presented simulations of the first galaxies in a representative volume of the universe. The simulations are unique because we model feedback-regulated galaxy formation, using time-dependent, spatially inhomogeneous radiative transfer coupled to hydrodynamics. Here we study the properties of simulated primordial dwarf galaxies with masses <~2×108 Msolar and investigate their impact on the intergalactic medium. While many primordial galaxies are dark, about 100-500 per comoving Mpc3 are luminous but relatively faint. They form preferentially in chain structures and have low surface brightness stellar spheroids extending to 20% of the virial radius. Their interstellar medium has mean density nH~10-100 cm-3, metallicity Z~0.01-0.1 Zsolar, and can sustain a multiphase structure. With large scatter, the mean efficiency of star formation scales with halo mass, <f*>~M2DM, independent of redshift. Because of feedback, halos smaller than a critical mass, Mcrit(z), are devoid of most of their baryons. More interestingly, we find that dark halos have always a smaller Mcrit(z) than luminous ones. Metal enrichment of the intergalactic medium is inhomogeneous, with only a 1%-10% volume filling factor of enriched gas with [Z/H]>-3.0 and 10%-50% with [Z/H]>-5.0. At z~10, the fraction of stars with metallicity Z<10-3 Zsolar is 10-6 of the total stellar mass. However, this study focuses on the effects of radiative feedback: mechanical feedback from SN explosions is only included in two of the seven simulations we have analyzed. Although detections of high-redshift dwarf galaxies with the James Webb Space Telescope will be a challenge, studies of their fossil records in the local universe are promising because of their large spatial density.
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