Effect of Lyα Radiative Transfer on Intensity Mapping Power Spectra

Abstract

Clustering of Lyα-emitting galaxies (LAEs) and Lyα line intensity mapping (LIM) are useful probes of cosmology. However, Lyα radiative transfer (RT) effects, such as absorption, line shift, and line broadening, and their dependence on the large-scale density and velocity fields can modify the measured LAE clustering and LIM statistics. We explore the effects of RT on the Lyα LIM power spectrum in two ways: using an analytic description based on linear approximations, and using lognormal mocks. The qualitative effects of intergalactic Lyα absorption on the LIM auto- and cross-power spectrum include a scale-dependent, reduced effective bias, reduced mean intensity, and modified redshift-space distortions. The linear absorption model does not describe the results of the lognormal simulations well. The random line shift suppresses the redshift-space power spectrum similar to the Fingers-of-God effect. In cross-correlation of LAEs or Lyα intensity with a non-Lyα tracer, the Lyα line shift leads to a phase shift of the complex power spectrum, i.e., a cosine damping of the real part. We study the impact of Lyα RT effects on the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) LAE and LIM power spectra using lognormal mocks. We find that even small amounts of IGM absorption will significantly change the measured LAE auto-power spectrum. The LAE-intensity cross-power spectrum stays within the measurement uncertainty. Therefore, HETDEX will be able to constrain Lyα RT effects.