Baryon acoustic oscillations from HI intensity mapping: the importance of cross-correlations in the monopole and quadrupole

Abstract

Cosmological parameter estimation in the post-reionisation era via the radio emission of neutral hydrogen (Hi), is one of the key science goals of the forthcoming SKA Observatory (SKAO). In this paper, we explore detection capability for baryon acoustic oscillations (BAO) with a SKAO-like experimental set up, using a suite of 100 simulations inclusive of the main limitations from foreground contamination and poor angular resolution caused by the radio telescope beam. The latter represents a serious challenge for BAO detection with Hi intensity mapping, hence we investigate adopting a multipole expansion approach as a means for mitigating the BAO detection limitations caused by the broad single-dish beam. We also showcase the gains made from cross-correlating the Hi intensity mapping data with an overlapping spectroscopic galaxy survey, aiming to test the potential synergies between the SKA Project and other future cosmological experiments at optical/near-infrared wavelengths, like the Euclid satellite or the Dark Energy Spectroscopic Instrument. Whilst we were still able to achieve a ∼ 4.5σ detection of BAO features in auto-correlation despite the dominant beam effect, a cross-correlation can increase this to a ∼ 6σ detection. Furthermore, by adopting the widely studied multipole expansion formalism, we show that including the power spectrum quadrupole besides the monopole in a joint fit can approximately double the BAO detection significance. Despite not implementing a radialonly P (k ) analysis in favour of the three-dimensional P (k) and its multipoles, we were still able to obtain robust constraints on the radial Alcock-Paczynski parameter, but found that perpendicular parameter remains unconstrained and prior dominated due to beam effects.

Detecting the power spectrum turnover with HI intensity mapping

“…This means the density field will be mapped with low angular resolution ( 1 deg) due to the large beam associated with the relatively small 15 m SKAO dishes. This poor angular resolution has been shown to pose challenges for SKAO-related H IM experiments aiming to detect BAO (Villaescusa-Navarro et al 2017;Kennedy & Bull 2021;Avila et al 2021;Rubiola et al 2021). A power spectrum feature on larger scales than the BAO would be better suited for detection by H IM if a sufficiently wide survey is commissioned, as planned with MeerKLASS (Santos et al 2017).…”