Reionization and the Cosmic Dawn with the Square Kilometre Array (1210.0197v2)

Abstract: The Square Kilometre Array (SKA) will have a low frequency component (SKA-low) which has as one of its main science goals the study of the redshifted 21cm line from the earliest phases of star and galaxy formation in the Universe. This 21cm signal provides a new and unique window on both the formation of the first stars and accreting black holes and the later period of substantial ionization of the intergalactic medium. The signal will teach us fundamental new things about the earliest phases of structure formation, cosmology and even has the potential to lead to the discovery of new physical phenomena. Here we present a white paper with an overview of the science questions that SKA-low can address, how we plan to tackle these questions and what this implies for the basic design of the telescope.

• The paper introduces a technical framework using SKA to probe cosmic reionization and the emergence of early structures via the redshifted 21cm hydrogen line.
• It details methodologies such as tomography, power spectrum analysis, and higher-order statistics to map ionized regions and characterize early cosmic fluctuations.
• Advanced radio interferometric techniques are employed to overcome observational challenges, enhancing our understanding of the Universe’s ionization history.

Reionization and the Cosmic Dawn with the Square Kilometre Array

The paper "Reionization and the Cosmic Dawn with the Square Kilometre Array" provides an exploratory and technical framework regarding the paper of cosmic reionization using the Square Kilometre Array (SKA). The SKA, with its advanced observational capacities, serves as a promising instrument to probe the early Universe's epochs, particularly the periods known as the Cosmic Dawn and the Epoch of Reionization.

A focal point of the research is the hydrogen 21cm line, redshifted due to the expansion of the Universe, which SKA will be uniquely equipped to observe. This line is crucial for several reasons. It reveals information about the formation of the first stars, galaxies, and black holes and traces the ionization of the intergalactic medium (IGM). By analyzing the 21cm signal, researchers aim to investigate the earliest structures in the Universe's formation and explore potential new physical phenomena.

The period of interest is divided into two phases based on the astrophysical processes involved:

1. Cosmic Dawn: This period marks the emergence of the first stars and accreting black holes. These early objects are pivotal in changing the quantum state of the neutral IGM, introducing new energy scales and ionizing photons which are crucial to this paper.
2. Epoch of Reionization: Subsequently, this period witnesses the substantial ionization of the IGM, led by radiation from galaxies. The SKA aims to capture the distribution and evolution of ionized regions across cosmic scales during this epoch.

Scientific Objectives and Methodologies:

• Tomography and Imaging: The SKA will perform detailed tomography of the 21cm signal, allowing for the mapping of the three-dimensional structure of the hydrogen distribution. This will enable the direct imaging of ionized bubbles, providing insights into the topology of the reionization.
• Power Spectrum Analysis: This method will be employed to statistically characterize the scale-dependent structure of the 21cm fluctuations. It supports the investigation of cosmological parameters and helps differentiate between various reionization sources by analyzing the scale of quantum fluctuations.
• Higher-Order Statistics: These statistical measures will be harnessed to capture non-Gaussian features in the 21cm data, offering complementary insights beyond the power spectrum, particularly relevant during the non-linear stages of reionization.
• Radio Interferometric Techniques: Advanced interferometric techniques are crucial for overcoming the challenges posed by foreground emissions, the ionosphere, and radio frequency interference. Techniques will include spatial and frequency filtering, model fitting, and leveraging the geometric configurations of the array.

Anticipated Outcomes and Implications:

The SKA's exploration of the Cosmic Dawn and Reionization is expected to:

• Yield a comprehensive map of early cosmic structures, tracing the ionization history of the Universe, which informs the evolution of large-scale structures.
• Enhance our understanding of fundamental cosmological models by providing constraints on high-redshift phenomena.
• Potentially discover new astrophysical phenomena linked with the complex interplay of radiation and matter in the early Universe.

Concluding Recommendations:

To accomplish these ambitious scientific goals, a highly optimized SKA configuration is necessary. Recommendations for the array design include:

• Frequency Range: Observational frequencies of 40–240 MHz to capture the entire critical periods of reionization.
• Array Configuration: A dense core with extended baselines to facilitate both imaging and power spectrum analyses, emphasizing a balance between compactness for sensitivity and extension for resolution.

This research guide not only elucidates the SKA’s potential in cosmic discoveries but also serves as a crucial step toward refining the broader cosmological context of reionization and early Universe phenomena.

In summary, the paper leverages SKA’s capacity to transcend prior observational limitations, offering unprecedented insight into the intergalactic medium's transformation during the pivotal phases in the Universe's evolution.