SCUBA-2

SCUBA-2
Name	SCUBA-2
Type	Submillimetre camera
Operator	University of Cambridge / Joint Astronomy Centre / UK Astronomy Technology Centre
Location	Mauna Kea Observatory / James Clerk Maxwell Telescope
Wavelength	450 µm, 850 µm
Detectors	Transition edge sensors
First light	2011

SCUBA-2 is a wide-field submillimetre imaging camera built for the James Clerk Maxwell Telescope on Mauna Kea Observatory that replaced an earlier bolometer array to provide unprecedented mapping speed at 450 µm and 850 µm. The instrument was developed by teams at the University of Cambridge, UK Astronomy Technology Centre, and collaborators including the Joint Astronomy Centre to enable surveys of star-forming regions, galaxies, and cold dust in the Milky Way and extragalactic sky. SCUBA-2's large-format arrays of transition edge sensor detectors and custom cryogenics advanced instrumentation capabilities for facilities such as the Submillimeter Array and influenced design choices for projects like the Atacama Large Millimeter/submillimeter Array.

Overview

SCUBA-2 provided wide-field continuum imaging at submillimetre wavelengths primarily to study star formation in regions like the Orion Nebula and Taurus molecular cloud, the evolution of galaxies across cosmic time including submillimetre galaxies, and dust in nearby systems such as Andromeda Galaxy and Messier 82. The project responded to scientific drivers from surveys planned by consortia including the SCUBA-2 All Sky Survey and follow-up programs tied to missions like Herschel Space Observatory and facilities such as Spitzer Space Telescope, Keck Observatory, and the Very Large Array.

Design and Instrumentation

SCUBA-2's focal plane comprised four 32×40 sub-arrays of superconducting transition edge sensor bolometers cooled to ~100 mK in a cryostat developed at institutions including the Institute of Astronomy, Cambridge and the National Physical Laboratory. Optical coupling used cold reimaging optics derived from designs in the Submillimeter Common-User Bolometer Array era and employed dichroic beam splitters to deliver simultaneous 450 µm and 850 µm bands compatible with the James Clerk Maxwell Telescope telescope optics. The readout system integrated time-domain multiplexing and electronics influenced by developments at the European Southern Observatory and the National Radio Astronomy Observatory to manage thousands of channels. The instrument incorporated mechanical and thermal technologies used previously in projects such as the Planck (spacecraft) detectors and ground-based instruments like the Bolocam camera.

Observing Modes and Data Reduction

SCUBA-2 supported scanning modes including "pong", "daisy", and raster patterns tailored for mapping scales used by surveys like the Gould Belt Survey and targeted programs on objects such as ULIRGs. Observing strategies were coordinated with scheduling systems at the Joint Astronomy Centre and leveraged atmospheric monitoring from nearby facilities including the CSO site instrumentation for precipitable water vapour estimation. Data reduction employed the SMURF package developed within the Starlink project and pipeline processing at the East Asian Observatory and CADC-style archives, building on algorithms from the Common Astronomy Software Applications environment to remove correlated noise, recover extended emission, and calibrate flux density.

Scientific Goals and Discoveries

Science goals targeted the mass function of prestellar cores in clouds like Perseus and Ophiuchus to test theories from researchers associated with Cambridge University and institutes such as the Max Planck Institute for Astronomy. SCUBA-2 surveys uncovered populations of cold, dense cores, contributed to constraints on the initial mass function in cluster-forming regions, and aided identification of high-redshift dusty star-forming galaxies later studied with ALMA and the Karl G. Jansky Very Large Array. Results informed models developed at the Institute of Astronomy, Cambridge and the Harvard-Smithsonian Center for Astrophysics and were cited in comparative studies involving the Hubble Space Telescope and Chandra X-ray Observatory.

Calibration and Performance

Flux calibration referenced standards such as Uranus and Neptune and used compact sources characterized by teams at the Royal Observatory, Edinburgh and the National Institute of Standards and Technology. Beam characterization and pointing tied into the James Clerk Maxwell Telescope engineering telemetry and benefited from cross-calibration with instruments on the Submillimeter Array and photometric datasets from the Spitzer Space Telescope. Measured sensitivities and mapping speeds were reported by instrument teams at conferences hosted by organizations like the Royal Astronomical Society and matched simulations performed by groups affiliated with the Science and Technology Facilities Council.

Operational History and Deployment

Commissioning and science operations began after first-light campaigns in 2011 under management by the Joint Astronomy Centre and stakeholder institutions including the UK Astronomy Technology Centre. SCUBA-2 operated through scheduled observing semesters coordinated with the Canadian Astronomy Data Centre and saw wide use by principal investigators from institutions such as the University of Exeter, University of Hertfordshire, and international partners in Japan and Canada. Operational lessons influenced upgrades at the James Clerk Maxwell Telescope and informed proposals for successors at facilities including the Large Millimetre Telescope and concepts for next-generation submillimetre cameras.

Collaborations and Supporting Facilities

The SCUBA-2 consortium included the University of Cambridge, UK Astronomy Technology Centre, Joint Astronomy Centre, the National Research Council (Canada), and partners from institutions such as the Max Planck Institute for Radio Astronomy and universities across Europe and North America. Supporting facilities for follow-up and complementary data included the Herschel Space Observatory, ALMA, VLA, Keck Observatory, and archives at the Canadian Astronomy Data Centre and the European Space Agency. Collaborative workshops and data releases were coordinated under auspices of meetings held by the International Astronomical Union and organizations including the Royal Astronomical Society.

Category:Submillimetre astronomy instruments