Effect of observing depth, field of view, and galaxy survey type on the signal-to-noise ratio of a cross-power spectrum detection. Each panel corresponds to a different galaxy survey type, which determines the mean redshift uncertainty associated with that survey. On the top axis of the slit spectroscopy panel, we show the corresponding rest frame UV magnitude limit required for ≥2σ completeness of the photometric candidate sample (see Fig. 7). Blue stars correspond to the SILVERRUSH and MOONRISE high-redshift galaxy surveys, and the orange star corresponds to an overlap of the Roman HLS survey and a single SKA-low AA* beam; multiple 21-cm fields can be tiled to increase the S/N in quadrature as discussed in the text. The MOONRISE spectroscopic survey should enable a 3σ detection of the cross-spectrum. In the spectroscopy panel we also show 100- and 1000-hour isochrones for potential future surveys using MOSAIC on the ELT.