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The First Galaxies: Assembly under Radiative Feedback from the First Stars

, , and . (2012)cite arxiv:1208.3698Comment: 25 pages, 13 figures, submitted to ApJ.

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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[1208.3698] The First Galaxies: Assembly under Radiative Feedback from the First Stars

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