SILVERRUSH. VI. A simulation of Lyα emitters in the reionization epoch and a comparison with Subaru Hyper Suprime-Cam survey early data

The survey of Lyman a emitters (LAEs) with the Subaru Hyper Suprime-Cam, called SILVERRUSH (Ouchi et al. 2018, PASJ, 70, S13), is producing massive data of LAEs at z6. Here we present LAE simulations to compare the SILVERRUSH data. In 162³ comoving Mpc³ boxes, where numerical radiative transfer calculations of reionization were performed, LAEs have been modeled with physically motivated analytic recipes as a function of halo mass. We have examined 2³ models depending on the presence or absence of dispersion of halo Lya emissivity, dispersion of the halo Lya optical depth, τ_α, and halo mass dependence of τ_α. The unique free parameter in our model, a pivot value of τ_α, is calibrated so as to reproduce the z = 5.7 Lya luminosity function (LF) of SILVERRUSH. We compare our model predictions with Lya LFs at z = 6.6 and 7.3, LAE angular auto-correlation functions (ACFs) at z = 5.7 and 6.6, and LAE fractions in Lyman break galaxies at 5 < z < 7. The Lya LFs and ACFs are reproduced by multiple models, but the LAE fraction turns out to be the most critical test. The dispersion of τ_α and the halo mass dependence of τ_α are essential to explain all observations reasonably. Therefore, a simple model of one-to-one correspondence between halo mass and Lya luminosity with a constant Lya escape fraction has been ruled out. Based on our best model, we presenτ_α formula to estimate the intergalactic neutral hydrogen fraction, xH I, from the observed Lya luminosity density at z ≳ 6. We finally obtain x_HI = 0.5^+0.1_-0.3 as a volume-average at z = 7.3.