Probing the nature of dark energy with 21-cm intensity mapping.

Abstract

Two approaches to measure the BAOs (baryon acoustic oscillations) with optical and radio telescopes, namely; galaxy redshift and intensity mapping (IM) surveys have been introduced and discussed in the literature. Among the two methods, the galaxy redshift survey has been used to great effect and is based on the detection and survey of millions of individual galaxies and measuring their redshifts by comparing templates of the spectral energy distributions of the light emitted from the galaxies with optical lines. IM is novel but a robust approach that focuses on surveys of extremely large volumes of galaxies without resolving each individual galaxy and can efficiently probe scales over redshift ranges inaccessible to the current galaxy redshift surveys. However, the IM survey has promisingly shown to have better overall sensitivity to the BAOs than the galaxy redshift survey but has a number of serious issues to be quantified. The most obvious of these issues is the presence of foreground contaminants from the Milky Way galaxy and extragalactic point sources which strongly dominate the neutral hydrogen (Hi) signal of our interest. Under this study, we are interested to realize the IM approach, pave the pathway, and optimize the scientific outputs of future radio experiments. We, therefore, carry out simulations and present forecasts of the cosmological constraints by employing Hi IM technique with three near-term radio telescopes by assuming 1 year of observational time. The telescopes considered here are Five-hundred-meter Aperture Spherical radio Telescope (FAST), BAOs In Neutral Gas Observations (BINGO), and Square Kilometre Array Phase I (SKA-I) single-dish experiments. We further forecast the combined constraints of the three radio telescopes with Planck measurements. In order to tackle the foreground challenge, we develop strategies to model various sky components and employ an approach to clean them from our Milky Way galaxy and extragalactic point sources by considering a typical single-dish radio telescope. Particularly, the Principal Component Analysis foreground separation approach considered can indeed recover the cosmological Hi signal to high precision. We show that, although the approach may face some challenges, it can be fully realized on the selected range of angular scales.