Prof. David Alonso

Abstract:

21 cm intensity mapping experiments aim to observe the diffuse neutral hydrogen (HI) distribution on large scales which traces the Cosmic structure. The Square Kilometre Array (SKA) will have the capacity to measure the 21 cm signal over a large fraction of the sky. However, the redshifted 21 cm signal in the respective frequencies is faint compared to the Galactic foregrounds produced by synchrotron and free-free electron emission. In this article, we review selected foreground subtraction methods suggested to effectively separate the 21 cm signal from the foregrounds with intensity mapping simulations or data. We simulate an intensity mapping experiment feasible with SKA phase 1 including extragalactic and Galactic foregrounds. We give an example of the residuals of the foreground subtraction with a independent component analysis and show that the angular power spectrum is recovered within the statistical errors on most scales. Additionally, the scale of the Baryon Acoustic Oscillations is shown to be unaffected by foreground subtraction.

Abstract:

This chapter describes the assumed specifications and sensitivities for HI galaxy surveys with SKA1 and SKA2. It addresses the expected galaxy number densities based on available simulations as well as the clustering bias over the underlying dark matter. It is shown that a SKA1 HI galaxy survey should be able to find around 5×106 galaxies over 5,000 deg2 (up to z ∼ 0:8), while SKA2 should find ∼ 109 galaxies over 30,000 deg2 (up to z ∼ 2:5). The numbers presented here have been used throughout the cosmology chapters for forecasting.

Abstract:

In this paper, we present a new method to extract cosmological parameters using the radial scale of the baryon acoustic oscillations as a standard ruler in deep galaxy surveys. The method consists of an empirical parametrization of the radial two-point correlation function, which provides a robust and precise extraction of the sound horizon scale at the baryon drag epoch. Moreover, it uses data from galaxy surveys in a manner that is fully cosmology independent and therefore unbiased. A study of the main systematic errors and the validation of the method in cosmological simulations are also presented, showing that the measurement is limited only by cosmic variance. We then study the full information contained in the baryon acoustic oscillations, obtaining that the combination of the radial and angular determinations of this scale is a very sensitive probe of cosmological parameters, able to set strong constraints on the dark energy properties, even without combining it with any other probe. We compare the results obtained using this method with those from more traditional approaches, showing that the sensitivity to the cosmological parameters is of the same order, while the measurements use only observable quantities and are fully cosmology independent.