SCUBA-2 and the SASSy All-Sky Survey
In the realm of submillimeter astronomy, the ability to detect cold gas and dust is essential for understanding the birth of stars and the evolution of galaxies. The SCUBA-2 camera, commissioned in 2011, represents a quantum leap in this capability. As a continuum instrument—one that measures the intensity of radiation over a range of wavelengths—SCUBA-2 allows astronomers to map the heavens with unprecedented speed and precision.
The Technology Behind SCUBA-2
SCUBA-2 is a ground-breaking camera utilizing large arrays of superconducting transition edge sensors (highly sensitive thermometers that detect the heat from incoming photons). This technology provides a mapping speed hundreds of times faster than its predecessor, SCUBA.
The instrument features a total of 10,240 pixels, split into two arrays of 5,120 elements each, operating at wavelengths of 450 and 850 microns. To expand its scientific utility, SCUBA-2 is supported by two ancillary instruments: FTS-2, which provides spectroscopic capabilities, and POL-2, which adds polarimetric capabilities.
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The SCUBA-2 All-Sky Survey (SASSy)
Launched in 2011, the SCUBA-2 All-Sky Survey, or SASSy, is a major legacy project conducted via the James Clerk Maxwell Telescope (JCMT) in Hawaii. The survey specifically maps the sky at 850 μm, a wavelength particularly sensitive to very cold gas and dust.
SASSy is one of the most significant legacy surveys on the JCMT, ranking as the second-largest in terms of telescope time, with a notional facility value exceeding £1 million. A global collaboration of approximately 50 astronomers from the United Kingdom, Canada, the United States, Netherlands, and Japan leads the effort to identify rare galaxies and regions of active star formation.
Unprecedented Resolution
One of the most striking achievements of SASSy is its angular resolution—the ability to distinguish small details in the sky. SASSy achieves a resolution of 14 arcseconds. To put this in perspective, it is 1,800 times more detailed than the previous best full-sky sub-mm map provided by COBE, which had a resolution of 7° (25,200 arcseconds).
It is important to note that because the JCMT is located in Hawaii, the survey cannot map the southernmost areas of the sky, as they are not visible from that latitude.
Scientific Objectives and Goals
The SASSy project is designed to answer fundamental questions about the composition and structure of the universe. Its primary goals include:
- Galactic Research: Determining the number of bright sub-mm galaxies, the fraction of lens sub-mm sources, and searching for undiscovered populations of extreme luminosity or cold local galaxies.
- Stellar Formation: Investigating the distribution and number of infrared dark clouds in our Galaxy and their relationship to Galactic structure and star formation.
- Star Formation Patterns: Analyzing the ratio of clustered versus isolated star formation and addressing the distributed T-Tauri problem.
- Satellite Calibration: Assisting in the calibration and foreground subtraction for the Planck microwave background satellite.
Key Facts
- Commission Date: SCUBA-2 was commissioned in 2011 and opened for general observations in February 2012.
- Pixel Count: 10,240 total pixels (5,120 at 450 μm and 5,120 at 850 μm).
- Resolution: 14 arcseconds, a massive improvement over COBE's 7° resolution.
- Primary Target: Cold gas and dust in the universe.
- Location: James Clerk Maxwell Telescope (JCMT), Hawaii.
| Feature | Specification / Detail |
|---|---|
| Sensor Type | Superconducting Transition Edge Sensors |
| Wavelengths | 450 μm and 850 μm |
| Total Pixels | 10,240 |
| SASSy Resolution | 14 arcseconds |
| Ancillary Tools | FTS-2 (Spectroscopy) and POL-2 (Polarimetry) |
Frequently Asked Questions
What is the primary purpose of the SASSy survey?
The SCUBA-2 All-Sky Survey (SASSy) aims to map the sky at 850 μm to detect very cold gas and dust, helping astronomers find rare galaxies and observe the process of star formation.
How does SCUBA-2 differ from the original SCUBA?
SCUBA-2 features a mapping speed that is hundreds of times faster than the original SCUBA, thanks to its large arrays of superconducting transition edge sensors.
Why can't SASSy map the entire sky?
Because the instrument is located at the James Clerk Maxwell Telescope in Hawaii, the southernmost regions of the sky are physically invisible from that location.
Who leads the SASSy collaboration?
The project was initially led by Dr. Mark Thompson and Dr. Stephen Serjeant, and has since expanded to include Dr. Tim Jenness and Prof. Douglas Scott as part of a four-person coordinating team.
How does SASSy help other space missions?
The data gathered by the SASSy project assists in the calibration and foreground subtraction for the Planck microwave background satellite.