English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The formation of the first stars out of metal-free gas appears to result instars at least an order of magnitude more massive than in the present-day case.We here consider what controls the transition from a primordial to a moderninitial mass function. It has been proposed that this occurs when effectivemetal line cooling occurs at a metallicity threshold of Z/Z_sun > 10^{-3.5}. Westudy the influence of low levels of metal enrichment on the cooling andcollapse of initially ionized gas in small protogalactic halos usingthree-dimensional, smoothed particle hydrodynamics simulations with particlesplitting. Our initial conditions represent protogalaxies forming within apreviously ionized H ii region that has not yet had time to cool and recombine.These differ considerably from those used in simulations predicting ametallicity threshold, where the gas was initially cold and only partiallyionized. In the centrally condensed potential that we study here, a widevariety of initial conditions for the gas yield a monolithic central collapse.Our models show no fragmentation during collapse to number densities as high as10^5 cm^{-3}, for metallicities reaching as high as 10^{-1} Z_sun in onerotating case, far above the threshold suggested by previous work. Rotationallows for the formation of gravitationally stable gas disks over largefractions of the local Hubble time. Turbulence slows the growth of the centraldensity slightly, but both spherically symmetric and turbulent initialconditions collapse and form a single sink particle. We therefore argue thatfragmentation at moderate density depends on the initial conditions for starformation more than on the metal abundances present.

Star Formation at Very Low Metallicity. V. The Greater Importance of Initial Conditions Compared to Metallicity Thresholds