AT20G survey

AT20G survey
Name	AT20G
Country	Australia
Frequency	20 GHz
Telescope	Australia Telescope Compact Array
Years	2004–2008
Sources	~6,000
Resolution	10–30 arcsec

AT20G survey The AT20G survey was a high-frequency radio survey conducted with the Australia Telescope Compact Array, designed to catalogue southern-sky compact sources at 20 gigahertz. It provided an all-southern-sky complement to northern surveys such as the Sloan Digital Sky Survey follow-ups and complemented low-frequency programs like the NRAO VLA Sky Survey and the Sydney University Molonglo Sky Survey. The project informed multiwavelength studies involving facilities such as Fermi Gamma-ray Space Telescope, Planck, and the Chandra X-ray Observatory.

Overview

The survey targeted declinations south of 0°, covering regions overlapping with observations from the Two Micron All Sky Survey, WISE, and the Gaia mission to enable cross-matching across radio, infrared, and optical catalogs. Principal investigators included staff from the Commonwealth Scientific and Industrial Research Organisation and the University of Sydney, collaborating with teams associated with the ATNF (Australia Telescope National Facility) and the CSIRO Radiophysics Laboratory. The AT20G program aimed to probe populations comparable to those studied by the Very Large Array legacy programs and to support follow-up by instruments such as the Very Long Baseline Array and the European Southern Observatory facilities.

Survey Design and Observations

The survey used the Australia Telescope Compact Array in fast-scanning mode with a compact configuration to detect flat-spectrum cores similar to those catalogued by the Green Bank Telescope surveys. Observations were scheduled to coordinate with calibration tied to standards like the Mars (planet) models and flux references used by the Perley–Butler scale adopted by other radio observatories. Sky coverage strategies mirrored tiling approaches employed by the Parkes Radio Telescope continuum surveys and leveraged experience from the Millimetre Astronomy Legacy Team programs. Observing campaigns operated alongside campaigns by the Fornax Cluster and Magellanic Clouds programs to maximize time allocation efficiency.

Data Processing and Catalog

Raw visibilities were reduced using pipelines based on software packages maintained by the Australia Telescope National Facility and methodologies comparable to the Common Astronomy Software Applications approach. Imaging and source extraction produced a catalog with positions and flux densities analogous in scope to the catalogs from NRAO projects and cross-identifications with the 6dF Galaxy Survey and 2dF Galaxy Redshift Survey. The catalog entries included polarisation measurements and variability flags, enabling associations with objects in the ROSAT and Hipparcos era databases. Quality control referenced procedures from the European Southern Observatory data validation protocols and statistical practices used by the Max Planck Institute for Radio Astronomy collaborations.

Scientific Results

The survey revealed a population dominated by flat-spectrum radio quasars and blazars similar to sources identified in Large Area Telescope work with the Fermi Gamma-ray Space Telescope and studies connected to the Compton Gamma Ray Observatory. Results influenced studies of active nuclei in samples overlapping with Seyfert galaxies catalogs, blazar samples compiled by the MOJAVE program, and compact steep-spectrum source investigations at observatories such as the National Radio Astronomy Observatory. AT20G data contributed to spectral energy distribution modeling used in analyses by teams associated with the Harvard–Smithsonian Center for Astrophysics and the Max Planck Institute for Astrophysics, and to variability studies complementing monitoring by the RATAN-600 and the Owens Valley Radio Observatory.

Follow-up Observations and Legacy

Follow-up programs employed the Very Long Baseline Array for milli-arcsecond imaging, the Gemini Observatory for optical spectroscopy, and the Hubble Space Telescope for host galaxy characterization in selected samples. The survey legacy informed subsequent high-frequency efforts at facilities like the Atacama Large Millimeter/submillimeter Array and the South African Radio Astronomy Observatory, and bolstered multi-messenger initiatives linked to the IceCube Neutrino Observatory and transient patrols by the Zwicky Transient Facility. Data products have been used by researchers at the University of Oxford, Harvard University, and the Australian National University in studies of source evolution and cosmological source counts.

Instrumentation and Calibration

The instrument suite included the Compact Array Broadband Backend with receivers comparable in sensitivity to those deployed at the Karl G. Jansky Very Large Array and calibration strategies borrowing from practices at the Submillimeter Array and Plateau de Bure Interferometer. Flux density scale and polarization calibration referenced models of primary calibrators such as PKS B1934-638 and tied into transfer standards used by the International Celestial Reference Frame maintenance teams. Beam characterization and error analysis incorporated methods from the Square Kilometre Array precursor projects and the Australian SKA Pathfinder development work.

Category:Radio astronomy surveys Category:Australia Telescope Compact Array projects