Optimal survey parameters: Ly αand H αintensity mapping for synergy with the 21-cm signal during reionization

Abstract

ABSTRACTIntensity mapping (IM) of multiple emission lines is emerging as a new branch to astronomy, to probe both properties of ionizing sources and the medium between, in particular the intergalactic medium. For Epoch of Reionization (EoR) studies, both multiline experiments and analysis methods are still in their infancy. Here we explore optimal survey parameters for Ly α (and H α) IM up to high redshifts of reionization, and requirements for optimized synergy with 21-cm experiments. We investigate line sensitivity, spectral resolution, and detector pixel size requirements for optimal (high signal-to-noise ratio, S/N) mission output. Power and cross-power spectra in a fiducial setup are derived, as are mock intensity maps. For line power spectrum measurements, a cumulative S/N of O(103), and for respective cross-spectra with SKA 21-cm observations of O(10) to O(102) are possible per redshift bin around the mid-point of reionization. These high S/N tomographic measurements are in reach for line sensitivities >8 × 10−18 erg s−1 sr−1 Hz−1, spectral resolution R > 250 and detector pixel sizes $\lt 2\,$ arcsec; all three requirements are met by the proposed Cosmic Dawn Intensity Mapper (CDIM). For CDIM, similar S/N values are in reach for H α. Already the planned NASA mission SPHEREx will detect during the EoR Ly α autopower and cross-power with 21-cm (SKA and HERA-type), for sensitivities >10−18 erg s−1 sr−1 Hz−1 in a moderate 21-cm foreground scenario (>10−17 erg s−1 sr−1 Hz−1 in an optimistic scenario). We advocate for IR missions in flavour of CDIM for a leap in IM and finish by providing a cookbook for successful multiline IM during the EoR.