Аннотация
Despite recent success in forming realistic disc galaxies at redshift zero,
simulations still form the bulk of their stars prematurely. We investigate the
process of stellar mass assembly in low-mass simulated galaxies, a dwarf and a
typical spiral, focusing on the effects of radiation from young stellar
clusters. We employ a novel model of star formation in which stars form
deterministically with a small efficiency per free-fall time, as observed in
molecular clouds. Stellar feedback includes radiation pressure from massive
stars and energy from supernova explosions and stellar winds. In galaxies with
masses up to those of typical spirals, radiation efficiently suppresses star
formation by dispersing and heating high density gas, mostly in the central
regions, preventing the formation of a massive bulge. Once the galaxies reach
this radiation-regulated growth regime, their global properties are robust to
the specific choice of model parameters. Only when radiative feedback is
included, do galaxies exhibit constant or even rising star formation histories,
forming more than 50% of their stars at z<1, an observed phenomenon that has so
far eluded analytical and numerical models. Low-mass galaxies with radiation
pressure have a factor of ~100 reduction in the star formation rate at z = 2,
and a factor of ~10 at z = 0.5. We conclude that radiation feedback is the main
mechanism that effectively decouples the growth of the galaxy from that of the
DM halo. Radiation does not affect the total baryon content of galaxies, but
instead maintains gas in a warm, low density phase where it cannot fuel star
formation. We find that the fraction of cold baryons within the simulated dwarf
galaxy is 20-30%, in agreement with THINGS. Lastly, unlike SN energy, radiation
from massive stars reduces the central density of the dark matter halo of a
galaxy with M_* ~10^8 M_sun, in support of recent observations.
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