Baryon acoustic oscillations in HI intensity mapping-galaxy clustering cross-correlation

Constraining cosmological parameters in the post-reionisation era (below redshift similar to 4-5) via the radio emission of neutral hydrogen, a technique known as Intensity Mapping (IM), is one of the main goals of the forthcoming Square Kilometer Array (SKA). Baryon Acoustic Oscillations (BAO) are a relatively large-scale phenomenon, for the most part captured by linear theory, unlikely to be imitated by other physical processes and depending on fundamental cosmological quantities (the sound horizon is a function of the Hubble parameter). All these features justify their role as a benchmark for future instruments which will look for their signal in the sky. Despite the low transverse resolution, their footprint may be recovered in the radial power spectrum, as already shown in the literature. Here we compare those results with the cross-correlation of IM and galaxy surveys, a possible future synergy between SKA and the ESA flagship mission Euclid.