Mon. Not. R. Astron. Soc., 450, 4207-4220 (2015/July-2)
The imprint of reionization on the star formation histories of dwarf galaxies.
BENITEZ-LLAMBAY A., NAVARRO J.F., ABADI M.G., GOTTLOBER S., YEPES G., HOFFMAN Y. and STEINMETZ M.
Abstract (from CDS):
We use a compilation of star formation histories (SFHs) and cosmological simulations to explore the impact of cosmic reionization on nearby isolated dwarf galaxies. Nearby dwarfs show a wide diversity of SFHs; from ancient systems that completed their star formation (SF) ∼ 10Gyr ago to young dwarfs that formed the majority of their stars in the past ∼ 5Gyr to `two-component' systems characterized by the overlap of old and young stars. As an ensemble, SF in nearby dwarfs dips to lower-than-average rates at intermediate times (4 < t/Gyr < 8), a feature caused in the simulation by cosmic reionization. Reionization heats the gas and drives it out of low-mass haloes, affecting especially systems with virial temperatures of ∼ 2x104K at zreion. SF begins before zreion in systems above this threshold; its associated feedback compounds the effects of reionization, emptying the haloes of gas and leaving behind old stellar systems. In haloes below the threshold at zreion, reionization leads to a delay in the onset of SF that lasts until the halo grows massive enough to allow gas to cool and form stars, leading to a system with a prominent young stellar component. `Two-component' systems may be traced to late accretion events that allow young stars to form in systems slightly above the threshold at zreion. The dearth of intermediate-age stars in nearby dwarfs might be the clearest signature of the imprint of cosmic reionization on the SFHs of dwarf galaxies.
© 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society (2015)
galaxies: dwarf - galaxies: evolution - galaxies: formation - Local Group - galaxies: stellar content - dark ages, reionization, first stars
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