[Paper Review] Science with SKA

F. Combes|arXiv (Cornell University)|Jul 8, 2021

Radio Astronomy Observations and Technology4 citations

TL;DR

This paper outlines how the Square Kilometre Array (SKA) will revolutionize cosmology, galaxy evolution, and astrobiology by leveraging HI-21cm line surveys, deep radio continuum imaging, and pulsar timing to probe dark energy, the Epoch of Reionization, and cosmic magnetism. It demonstrates that SKA-1 will deliver competitive, complementary constraints to optical surveys like Euclid, with breakthrough potential in measuring H₀, detecting nanohertz gravitational waves, and mapping pre-biotic molecules in protoplanetary disks via synergy with ALMA.

ABSTRACT

Highlights are presented about the science to be done with SKA. as well as state of the art science already done today with its precursors (MeerKAT, ASKAP) and pathfinders (LOFAR, NenuFAR), with accent on the expected breakthroughs.

Motivation & Objective

• To establish the scientific potential of the Square Kilometre Array (SKA) in addressing fundamental cosmological puzzles, including dark energy, dark matter, and the H₀ tension.
• To demonstrate that radio tracers such as HI-21cm emission and radio continuum provide complementary, bias-differentiated probes to optical surveys, enhancing cosmological parameter constraints.
• To investigate the Epoch of Reionization (EoR) using redshifted 21cm HI emission, uniquely accessible through SKA’s wide-field, deep surveys.
• To enable high-precision pulsar timing for detecting nanohertz gravitational waves and probing strong gravity, particularly via millisecond pulsars.
• To map cosmic magnetic fields and detect pre-biotic molecules in protoplanetary disks through synergy with ALMA, advancing the search for life’s origins.

Proposed method

• Utilizing SKA-1 and SKA-2 surveys to conduct all-sky and deep-field HI-21cm line surveys of galaxies, detecting up to 4 million galaxies up to z=0.2 and 0.4 million up to z=0.8.
• Applying weak lensing and redshift-space distortion (RSD) techniques to radio-continuum and HI-traced large-scale structures to constrain Ω and Λ evolution.
• Employing intensity mapping of HI over 30,000 square degrees up to z=3 to probe large-scale structure and cosmological parameters with high volume coverage.
• Using VLBI and maser line measurements (e.g., H₂O, OH) in active galactic nuclei to obtain precise distance indicators and test the H₀ discrepancy.
• Implementing pulsar timing arrays with SKA to detect low-frequency (nanoHz) gravitational waves from supermassive black hole binaries.
• Combining SKA-1 mid-frequency observations with ALMA at higher frequencies to detect complex organic molecules (COMs) such as CH₃OH, CH₂DOH, and NH₂CHO in protoplanetary disks.

Experimental results

Research questions

• RQ1 How can SKA’s HI-21cm surveys provide competitive and complementary constraints on dark energy and the H₀ tension compared to optical probes like Euclid?
• RQ2 To what extent can redshifted 21cm emission from neutral hydrogen map the Epoch of Reionization and trace the formation of the first galaxies?
• RQ3 Can SKA’s pulsar timing array detect nanohertz gravitational waves and provide evidence for primordial gravitational wave backgrounds?
• RQ4 What is the role of cosmic magnetic fields in galaxy formation, and how can SKA measure Faraday rotation and magnetic field structures across the cosmic web?
• RQ5 How can SKA and ALMA jointly detect and characterize pre-biotic molecules in protoplanetary disks, and what are the detectable column densities for key species like α-alanine?

Key findings

• SKA-1 will detect approximately 4 million galaxies up to z=0.2 in an all-sky survey, 2 million up to z=0.6 in wide-field surveys, and 0.4 million up to z=0.8 in deep fields, enabling high-precision cosmological clustering measurements.
• Intensity mapping over 30,000 square degrees with SKA-1 will cover redshifts up to z=3 and sample a volume significantly larger than optical surveys, making it highly competitive for BAO and RSD studies.
• SKA-1 will enable weak lensing measurements on a billion objects up to z=6, providing robust constraints on large-scale structure growth and dark energy evolution.
• The detection of 1000 hours of integration with SKA1-mid is expected to clearly detect α-alanine in protoplanetary disks, with a column density threshold of 10¹³ cm⁻².
• LOFAR and GLEAM surveys have already detected synchrotron emission in filaments at 15 Mpc scales with magnetic fields of 30–60 nG, suggesting enhanced shock acceleration and potential for larger-scale detection with SKA.
• Maser-based distance measurements from SKA-1 are expected to confirm the local H₀ value of ~73.9 km/s/Mpc, offering a complementary probe to Cepheid and Planck measurements and potentially resolving the 3.7σ tension in H₀.