Speaker
Grant Mathews
(Center for Astrophysics (CANDU), Department of Physics, University of Notre Dame, Notre Dame,)
Description
We present numerical simulations to describe the
nucleosynthesis and evolution of pre-Galactic clouds in a
model which is motivated by cold dark matter simulations of
hierarchical galaxy formation. We adopt a SN-induced
star-formation mechanism within a model that follows the
evolution of chemical enrichment and energy input to the
clouds by Type II and Type Ia supernovae.
We utilize metallicity-dependent yields for all elements at
all times, and include effects of finite stellar lifetimes.
We derive the metallicity distribution functions
for stars in the clouds, their age-metallicity relation, and
relative elemental abundances for a number of alpha- and
Fe-group elements. The stability of these
clouds against destruction is discussed, and results are
compared for different initial mass functions. We find that
the dispersion of the metallicity distribution
function observed in the outer halo is naturally reproduced
by contributions from many clouds with different initial
conditions. The scatter in metallicity as a
function of age for these stars is very large, implying that
no age-metallicity relation exists in the early stages of
galaxy formation.
Clouds with initial masses greater than that of presently
observed globular clusters are found to survive the
first 0.1 Gyr from the onset of star formation, suggesting
that such systems may have contributed to the formation of
the first stars, and could have been self-enriched.
More massive clouds are only stable when one assumes an
initial mass function that is not biased towards massive
stars, indicating that even if the first stars were formed
according to a top-heavy mass function, subsequent star
formation was likely to have proceeded with a present-day
mass function, or happened in an episodic manner. The
predicted relative abundances of some alpha- and Fe-group
elements show good
agreement with the observed values down to metallicities
below [Fe/H] = -4 when the iron yields are reduced relative
to stellar models. The observed scatter is also
reproduced for most elements including the observed
bifurcation in [alpha/Fe] for stars with low [Fe/H].
However, the predicted dispersion may be too large for some
elements (particularly alpha elements) unless a limited
range of progenitor masses contributing to the abundances of
these elements is assumed.
The contributions to the abundances from supernovae with
different progenitor masses and metallicity are
discussed. The results suggest that the low-mass end of
SNeII was probably absent at the very lowest metallicities,
and that the upper mass limit for the first stars that
contributed to nucleosynthesis may be < 40 solar masses.
Author
Grant Mathews
(Center for Astrophysics (CANDU), Department of Physics, University of Notre Dame, Notre Dame,)
Co-authors
Lamya Saleh
(Department of Physics & Astronomy, Northwestern University)
Timothy Beers
(MIchigan State University/Joint Institute for Nuclear Astrophysics)
