Modelling the observed luminosity function and clustering evolution of Ly α emitters: growing evidence for late reionization

Abstract

We model the high-redshift (z > 5) Ly α-emitting galaxy (LAE) population using the empirical rest-frame equivalent width distribution. We calibrate to the observed luminosity function and angular correlation function at z = 5.7 as measured by the SILVERRUSH survey. This allows us to populate the high-dynamic-range Sherwood simulation suite with LAEs, and to calculate the transmission of their Ly α emission through the intergalactic medium (IGM). We use this simulated population to explore the effect of the IGM on high-redshift observations of LAEs, and make predictions for the narrow-band filter redshifts at z = 6.6, 7.0, and 7.3. Comparing our model with existing observations, we find a late reionization is suggested, consistent with the recent low optical depth derived from the cosmic microwave background by the Planck collaboration and the opacity fluctuations in the Ly α forest. We also explore the role of the circumgalactic medium (CGM) and the large volume of gas that is infalling on to the host halo versus the IGM in attenuating the Ly α signal, finding that a significant fraction of the attenuation is due to the CGM and infalling gas, which increases towards the end of reionization, albeit with a large scatter across the mock LAE population.