The impact of Lyman-α radiative transfer on large-scale clustering in the Illustris simulation

Context. Lyman- α emitters (LAEs) are a promising probe of the large-scale structure at high redshift, z ≳ 2. In particular, the Hobby-Eberly Telescope Dark Energy Experiment aims at observing LAEs at 1.9 z α emission line generates an anisotropic selection bias in the LAE clustering on large scales, s ≳ 10 Mpc. This effect could potentially induce a systematic error in the BAO and RSD measurements. Also, there exists a recent claim to have observational evidence of the effect in the Lyman- α intensity map, albeit statistically insignificant. Aims. We aim at quantifying the impact of the Lyman- α RT on the large-scale galaxy clustering in detail. For this purpose, we study the correlations between the large-scale environment and the ratio of an apparent Lyman- α luminosity to an intrinsic one, which we call the “observed fraction”, at 2 z Methods. We apply our Lyman- α RT code by post-processing the full Illustris simulations. We simply assume that the intrinsic luminosity of the Lyman- α emission is proportional to the star formation rate of galaxies in Illustris, yielding a sufficiently large sample of LAEs to measure the anisotropic selection bias. Results. We find little correlation between large-scale environment and the observed fraction induced by the RT, and hence a smaller anisotropic selection bias than has previously been claimed. We argue that the anisotropy was overestimated in previous work due to insufficient spatial resolution; it is important to keep the resolution such that it resolves the high-density region down to the scale of the interstellar medium, that is, ~1 physical kpc. We also find that the correlation can be further enhanced by assumptions in modeling intrinsic Lyman- α emission.