Abstract
We investigate how radiative feedback from the first stars affects the
assembly of the first dwarf galaxies. To this end we perform cosmological
zoomed smoothed particle hydrodynamics simulations of a dwarf galaxy assembling
inside a halo reaching a virial mass 10^9 solar at z = 10. The simulations
follow the non-equilibrium chemistry/cooling of primordial gas and the
subsequent conversion of the gas into metal-free stars. To quantify the
radiative feedback, we compare a simulation in which stars emit both molecular
hydrogen dissociating and hydrogen/helium ionizing radiation with a simulation
in which stars emit only molecular hydrogen dissociating radiation, and further
with a simulation in which stars remain dark. Photodissociation and
photoionization exert a strong negative feedback on the assembly of the galaxy
inside the main minihalo progenitor. Gas condensation is strongly impeded, and
star formation is strongly suppressed in comparison with the simulation in
which stars remain dark. The feedback on the gas implies a suppression of the
central dark matter densities in the minihalo progenitor by factors of up to a
few, which is a significant deviation from the singular isothermal density
profile characterizing the dark matter distribution inside the virial radius in
the absence of radiative feedback. The evolution of gas densities, star
formation rates, and the distribution of dark matter becomes insensitive to the
inclusion of dissociating radiation in the late stages of the minihalo
assembly, and it becomes insensitive to the inclusion of ionizing radiation
once the minihalo turns into an atomically cooling galaxy. The formation of an
extended disk inside the dwarf galaxy is a robust outcome not affected by the
inclusion of radiation. We estimate that dwarf galaxies such as simulated here
will be among the faintest galaxies the upcoming James Webb Space Telescope
will detect.
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