Ostriker and Gnedin
[127]
have carried out high resolution numerical simulations of the
reheating and reionization of the Universe due to star formation
bursts triggered by molecular hydrogen cooling. Accounting for
the chemistry of the primeval hydrogen/helium plasma,
self-shielding of the gas, radiative cooling, and a
phenomenological model of star formation, they find that two
distinct star populations form: the first generation pop III
from
cooling prior to reheating at redshift
; and the second generation pop II at
when the virial temperature of the gas clumps reaches
and hydrogen line cooling becomes efficient. Star formation
slows in the intermittent epoch due to the depletion of
by photo-destruction and reheating. In addition, the objects
which formed pop III stars also initiate pop II
sequences when their virial temperatures reach
through continued mass accretion.
In resolving the details of a single star
forming region in a CDM Universe, Abel et al.
[2, 3]
implemented a non-equilibrium radiative cooling and chemistry
model
[1
, 21
]
together with the hydrodynamics and dark matter equations,
evolving nine separate atomic and molecular species (
,
,
,
,
,
,
,
, and
, according to the reactive network described in Section
6.4.1) on nested and adaptively refined numerical grids. They follow
the collapse and fragmentation of primordial clouds over many
decades in mass and spatial dynamical range, finding a core of
mass
forms from a halo of about
(where a significant number fraction of hydrogen molecules are
created) after less than one percent of the halo gas cools by
molecular line emission. Bromm et al.
[48
]
use a different Smoothed Particle Hydrodynamics (SPH) technique
and a six species model (
,
,
,
,
, and
) to investigate the initial mass function of the first
generation pop III stars. They evolve an isolated
peak of mass
which collapses at redshift
and forms clumps of mass
which then grow by accretion and merging, suggesting that the
very first stars were massive and in agreement with
[3]
.
Update
The implications of an early era of massive star populations on
the thermal and chemical state of the intergalactic medium was
investigated by Yoshida et al.
[164]
. They considered the effects of feedback and radiation transfer
in early structure formation simulations to show that a
significant fraction of the IGM can be ionized and polluted by
metals from the first stars to form and become supernovae by
, thus affecting subsequent stellar populations. They also argue
that observed elemental abundances in the intracluster medium are
not affected by metals originating from the first stars.
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