Institute of Astronomy

Star Formation at Very Low Metallicity

SpeakerTalk DateTalk Series
Anne-Katharina Jappsen, Cardiff4 February 2010Institute of Astronomy Colloquia

Abstract

In cold dark matter cosmological models, the first stars to form are believed to do
so within small
protogalaxies. We wish to understand how the evolution of these early protogalaxies
changes once the
gas forming them has been enriched with small quantities of heavy elements, which
are produced and
dispersed into the intergalactic medium by the first supernovae. We use
high-resolution hydrodynamic
simulations that incorporate the effects of the appropriate chemical and thermal
processes.
Our initial conditions represent protogalaxies forming within a fossil HII region, a
previously
ionized region that has not yet had time to cool and recombine. We study the
influence of low levels
of metal enrichment on the cooling and collapse of ionized gas in small
protogalactic halos using
three-dimensional, smoothed particle hydrodynamics simulations with particle
splitting.
In the centrally condensed potential that we study here, a wide variety of initial
conditions for
the gas yield a monolithic central collapse. Our models show no fragmentation during
collapse to
number densities as high as 10^5 cm^â^È^Ò3 for metallicities reaching as high as
10^â^È^Ò1 Z_sun, far above
the threshold suggested by previous work. We therefore argue that fragmentation at
moderate density
depends on the initial conditions for star formation more than on the metal
abundances present.

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