Bibcode
Wiersma, Robert P. C.; Schaye, Joop; Theuns, Tom; Dalla Vecchia, C.; Tornatore, Luca
Bibliographical reference
Monthly Notices of the Royal Astronomical Society, Volume 399, Issue 2, pp. 574-600.
Advertised on:
10
2009
Citations
585
Refereed citations
559
Description
We present an implementation of stellar evolution and chemical feedback
for smoothed particle hydrodynamics simulations. We consider the timed
release of individual elements by both massive (Type II supernovae and
stellar winds) and intermediate-mass stars (Type Ia supernovae and
asymptotic giant branch stars). We illustrate the results of our method
using a suite of cosmological simulations that include new prescriptions
for radiative cooling, star formation and galactic winds. Radiative
cooling is implemented element-by-element, in the presence of an
ionizing radiation background, and we track all 11 elements that
contribute significantly to the radiative cooling.
While all simulations presented here use a single set of physical
parameters, we take specific care to investigate the robustness of the
predictions of chemodynamical simulations with respect to the
ingredients, the methods and the numerical convergence. A comparison of
nucleosynthetic yields taken from the literature indicates that relative
abundance ratios may only be reliable at the factor of 2 level, even for
a fixed initial mass function. Abundances relative to iron are even more
uncertain because the rate of Type Ia supernovae is not well known. We
contrast two reasonable definitions of the metallicity of a resolution
element and find that while they agree for high metallicities, there are
large differences at low metallicities. We argue that the discrepancy is
indicative of the lack of metal mixing caused by the fact that metals
are stuck to particles. We argue that since this is a (numerical)
sampling problem, solving it by using a poorly constrained physical
process such as diffusion could have undesired consequences. We
demonstrate that the two metallicity definitions result in redshift z =
0 stellar masses that can differ by up to a factor of 2, because of the
sensitivity of the cooling rates to the elemental abundances.
Finally, we use several 5123 particle simulations to
investigate the evolution of the distribution of heavy elements, which
we find to be in reasonably good agreement with available observational
constraints. We find that by z = 0 most of the metals are locked up in
stars. The gaseous metals are distributed over a very wide range of gas
densities and temperatures. The shock-heated warm-hot intergalactic
medium has a relatively high metallicity of
~10-1Zsolar that evolves only weakly, and is
therefore an important reservoir of metals. Any census aiming to account
for most of the metal mass will have to take a wide variety of objects
and structures into account.