Аннотация
The ultraviolet background (UVB) emitted by quasars and galaxies governs the
ionization and thermal state of the intergalactic medium (IGM), regulates the
formation of high-redshift galaxies, and is thus a key quantity for modeling
cosmic reionization. The vast majority of cosmological hydrodynamical
simulations implement the UVB via a set of spatially uniform photoionization
and photoheating rates derived from UVB synthesis models. We show that
simulations using canonical UVB rates reionize, and perhaps more importantly,
spuriously heat the IGM, much earlier z ~ 15 than they should. This problem
arises because at z > 6, where observational constraints are non-existent, the
UVB amplitude is far too high. We introduce a new methodology to remedy this
issue, and generate self-consistent photoionization and photoheating rates to
model any chosen reionization history. Following this approach, we run a suite
of hydrodynamical simulations of different reionization scenarios, and explore
the impact of the timing of reionization and its concomitant heat injection on
the the thermal state of the IGM. We present a comprehensive study of the
pressure smoothing scale of IGM gas, illustrating its dependence on the details
of both hydrogen and helium reionization, and argue that it plays a fundamental
role in interpreting Lyman-alpha forest statistics and the thermal evolution of
the IGM. The premature IGM heating we have uncovered implies previous work has
likely dramatically overestimated the impact of photoionization feedback on
galaxy formation, which sets the minimum halo mass able to form stars at high
redshifts. We make our new UVB photoionization and photoheating rates publicly
available for use in future simulations.
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