The BlueTides Simulation: First Galaxies and Reionization
  We introduce the BlueTides simulation and report initial results for the
luminosity functions of the first galaxies and AGN, and their contribution to
reionization. BlueTides was run on the BlueWaters cluster at NCSA from $z=99$
to $z=8.0$ and includes 2$\times$7040$^3$ particles in a $400$Mpc/h per side
box, making it the largest hydrodynamic simulation ever performed at high
redshift. BlueTides includes a pressure-entropy formulation of smoothed
particle hydrodynamics, gas cooling, star formation (including molecular
hydrogen), black hole growth and models for stellar and AGN feedback processes.
The star formation rate density in the simulation is a good match to current
observational data at $z\sim 8-10$. We find good agreement between observations
and the predicted galaxy luminosity function in the currently observable range
$-18\le M_{\mathrm UV} \le -22.5$ with some dust extinction required to match
the abundance of brighter objects. BlueTides implements a patchy reionization
model that produces a fluctuating UV background. BlueTides predicts number
counts for galaxies fainter than current observational limits which are
consistent with extrapolating the faint end slope of the luminosity function
with a power law index $\alpha\sim -1.8$ at $z\sim 8$ and redshift dependence
of $\alpha\sim (1+z)^{-0.4}$. The AGN population has a luminosity function well
fit by a power law with a slope $\alpha\sim -2.4$ that compares favourably with
the deepest CANDELS-Goods fields. We investigate how these luminosity functions
affect the progress of reionization, and find that a high Lyman-$\alpha$ escape
fraction ($f_\mathrm{esc} \sim 0.5$) is required if galaxies dominate the
ionising photon budget during reionization. Smaller galaxy escape fractions
imply a large contribution from faint AGN (down to $M_\mathrm{UV}=-12$) which
results in a rapid reionization, disfavoured by current observations.
