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

Abstract

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, τα, and halo mass dependence of τα. The unique free parameter in our model, a pivot value of τα, 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 τα and the halo mass dependence of τα 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 presenτα formula to estimate the intergalactic neutral hydrogen fraction, xH I, from the observed Lya luminosity density at z ≳ 6. We finally obtain xHI = 0.5+0.1-0.3 as a volume-average at z = 7.3.