Beecroft Institute for Particle Astrophysics and Cosmology

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:

The imprint of baryon acoustic oscillations (BAO) in large-scale structure can be used as a standard ruler for mapping out the cosmic expansion history, and hence for testing cosmological models. In this chapter we briefly describe the scientific background to the BAO technique, and forecast the potential of the Phase 1 and 2 SKA telescopes to perform BAO surveys using both galaxy catalogues and intensity mapping, assessing their competitiveness with current and future optical galaxy surveys. We find that a 25,000 deg2 intensity mapping survey on a Phase 1 array will preferentially constrain the radial BAO, providing a highly competitive 2% constraint on the expansion rate at z ≃ 2. A 30,000 deg2 galaxy redshift survey on SKA2 will outperform all other planned experiments for z < ∼ 1:4.

Abstract:

The peculiar motion of galaxies can be a particularly sensitive probe of gravitational collapse. As such, it can be used to measure the dynamics of dark matter and dark energy as well the nature of the gravitational laws at play on cosmological scales. Peculiar motions manifest themselves as an overall anisotropy in the measured clustering signal as a function of the angle to the line-ofsight, known as redshift-space distortion (RSD). Limiting factors in this measurement include our ability to model non-linear galaxy motions on small scales and the complexities of galaxy bias. The anisotropy in the measured clustering pattern in redshift-space is also driven by the unknown distance factors at the redshift in question, the Alcock-Paczynski distortion. This weakens growth rate measurements, but permits an extra geometric probe of the Hubble expansion rate. In this short chapter we will briefly describe the scientific background to the RSD technique, and forecast the potential of the SKA phase 1 and the SKA2 to measure the growth rate using both galaxy catalogues and intensity mapping, assessing their competitiveness with current and future optical galaxy surveys.

Abstract:

This paper examines incidents of play, socialisation, fun and amusement to consider how these forms of social interaction relate to the serious gaming elements of the citizen science platform. Through an ethnographic study we reveal how participants of citizen science projects demonstrate aspccts of 'Gamiscd' behaviour. 'Gamised' behaviour is defined as user generated play in a digital platform and contrasts to incidents of 'gamification∗ where a platform designer purposely embeds games into a computer platform. The paper therefore examines incidents of play, socialisation, fun and amusement and compares them with the serious gaming elements of the citizen science platform.