[Paper Review] Science with ASKAP - the Australian Square Kilometre Array Pathfinder

S. Johnston, R. Taylor+48 more|ArXiv.org|Oct 29, 2008

Radio Astronomy Observations and TechnologyPhysics and Astronomy307 references250 citations

TL;DR

This paper outlines the scientific potential of the Australian Square Kilometre Array Pathfinder (ASKAP), a wide-field radio telescope using phased-array feed technology to conduct deep, large-area surveys of the sky at cm and m wavelengths. ASKAP is designed to detect up to a million galaxies in atomic hydrogen, 60 million in synchrotron emission, and over 500,000 polarized sources, enabling breakthroughs in galaxy evolution, cosmic magnetism, transient phenomena, and pulsar timing, while also serving as a technological precursor to the Square Kilometre Array (SKA).

ABSTRACT

[ABRIDGED VERSION] The future of cm and m-wave astronomy lies with the Square Kilometre Array (SKA), a telescope under development by a consortium of 17 countries. The SKA will be 50 times more sensitive than any existing radio facility. A majority of the key science for the SKA will be addressed through large-area imaging of the Universe at frequencies from 300 MHz to a few GHz. The Australian SKA Pathfinder (ASKAP) is aimed squarely in this frequency range, and achieves instantaneous wide-area imaging through the development and deployment of phase-array feed systems on parabolic reflectors. This large field-of-view makes ASKAP an unprecedented synoptic telescope poised to achieve substantial advances in SKA key science. The central core of ASKAP will be located at the Murchison Radio Observatory in inland Western Australia, one of the most radio-quiet locations on the Earth and one of the sites selected by the international community as a potential location for the SKA. Following an introductory description of ASKAP, this document contains 7 chapters describing specific science programmes for ASKAP. The combination of location, technological innovation and scientific program will ensure that ASKAP will be a world-leading radio astronomy facility, closely aligned with the scientific and technical direction of the SKA. A brief summary chapter emphasizes the point, and considers discovery space.

Motivation & Objective

• To demonstrate the scientific capabilities of ASKAP as a pathfinder for the Square Kilometre Array (SKA), focusing on large-area, wide-field surveys at frequencies from 300 MHz to a few GHz.
• To address key astrophysical questions on galaxy formation and evolution, magnetic field evolution, and the nature of the transient radio sky through high-sensitivity, wide-field observations.
• To establish a radio-quiet site in Western Australia for future SKA operations and to prototype technologies such as phased-array feeds for future SKA mid-frequency systems.
• To detect and characterize a million galaxies in HI emission, 60 million in synchrotron emission, and over 500,000 polarized sources to map cosmic evolution and magnetic fields across time.
• To discover and time a thousand new radio pulsars and monitor transient and variable radio sources, including gamma-ray burst afterglows and intra-day variables, to explore high-energy phenomena.

Proposed method

• Utilize phased-array feed systems on parabolic reflectors to achieve an instantaneous field of view of up to 30 square degrees, enabling rapid, wide-area sky surveys.
• Conduct deep, wide-area continuum and spectral line surveys across 300 MHz to a few GHz, targeting HI 21 cm emission and synchrotron radiation from galaxies.
• Implement high dynamic range imaging and high time-resolution processing to detect transient and variable sources on timescales from seconds to months.
• Apply interferometric synthesis with the Very Long Baseline Interferometry (VLBI) network to achieve high angular resolution for accurate source localization and follow-up.
• Use polarimetry to measure rotation measures across the sky, enabling the mapping of magnetic fields in galaxies and the intergalactic medium.
• Integrate real-time data processing pipelines to identify and flag transient candidates, prioritizing sources for follow-up across multiple wavelengths.

Experimental results

Research questions

• RQ1 What is the distribution and evolution of atomic hydrogen in galaxies out to a redshift of 0.2, and how does it inform galaxy formation and gas accretion processes?
• RQ2 How do magnetic fields in galaxies evolve over cosmic time, and what do large-scale rotation measure grids reveal about cosmic magnetic field structure?
• RQ3 What is the population and luminosity function of radio-emitting galaxies across cosmic time, and how do they trace star formation and AGN activity?
• RQ4 What new classes of transient or variable radio sources can be discovered with a wide-field, high-sensitivity survey, and how do they relate to high-energy phenomena?
• RQ5 Can ASKAP detect and time a thousand new radio pulsars, and how will this improve the sensitivity of global pulsar timing arrays for gravitational wave detection?

Key findings

• ASKAP is projected to detect up to one million galaxies in HI emission across 75% of the sky out to a redshift of 0.2, enabling a comprehensive census of gas-rich galaxies in the nearby Universe.
• The telescope is expected to detect synchrotron emission from approximately 60 million galaxies, providing a deep view of the radio-loud galaxy population and enabling cosmological tests via large-scale structure surveys.
• Over 500,000 polarized radio sources are expected to be detected, allowing the creation of a 10′-resolution grid of rotation measures to map magnetic fields in galaxies and the intergalactic medium.
• ASKAP’s wide field of view and sub-mJy sensitivity allow for single-day surveys of the entire sky, making it uniquely suited for detecting rare and transient radio phenomena.
• The instrument is expected to discover and time approximately 1,000 new radio pulsars, significantly enhancing the sensitivity of pulsar timing arrays for low-frequency gravitational wave detection.
• The combination of high sensitivity, wide field of view, and high time resolution positions ASKAP to discover new classes of transient sources, including potential new astrophysical phenomena such as fast radio bursts or radio counterparts to gamma-ray bursts.