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Dark energy camera takes first pictures

Photonics Spectra
Dec 2012
CERRO TOLOLO, Chile – After eight years in the making, the most powerful sky-mapping machine ever created, the 570-megapixel Dark Energy Camera (DECam), achieved first light on Sept. 12.

The camera was constructed at Fermi National Accelerator Laboratory in Batavia, Ill., and mounted on the Victor M. Blanco telescope at the National Science Foundation’s Cerro Tololo Inter-American Observatory, the southern branch of the US National Optical Astronomy Observatory. With this device, roughly the size of a phone booth, astronomers and physicists will probe the mystery of dark energy, the force they believe is causing the universe to expand faster and faster.

The most powerful sky-mapping machine ever created, the 570-megapixel Dark Energy Camera (DECam), is mounted on the Blanco telescope in Chile.

A photometric imaging camera, it measures the amount of light in various colors from astronomical objects rather than details of their spectra. It can see light from more than 100,000 galaxies up to 8 billion light-years away in each image. Its array of 62 CCDs has unprecedented sensitivity to red light.

Scientists in the Dark Energy Survey collaboration will use the camera to undertake the largest galaxy survey ever. They will use the data to carry out four probes of dark energy, studying galaxy clusters, supernovae, the large-scale clumping of galaxies and weak gravitational lensing. This will be the first time all four of these methods will be possible in a single experiment.

The Dark Energy Camera features 62 charged-coupled devices, which record a total of 570 megapixels per snapshot.

“The Dark Energy Survey will help us understand why the expansion of the universe is accelerating, rather than slowing, due to gravity,” said Brenna Flaugher, project manager and scientist at Fermilab. “It is extremely satisfying to see the efforts of all the people involved in this project finally come together.”

Fermilab turned to Lawrence Berkeley National Lab for the CCDs needed, realizing that the high-redshift galaxies they sought would require longer exposures to get secure photometric results. Berkley Lab’s CCDs have higher quantum efficiency in the near-infrared than typical astronomical CCDs.

Manufacture of the DECam CCDs was overseen by Steve Holland, a senior engineer in Berkeley Lab’s Engineering Div. who invented the Berkeley Lab CCD in the mid-1990s as a spinoff from research and development of detectors for high-energy physics.

“Fermilab was attracted to our CCDs because of their improved red response,” Holland said, “but considering that there were as yet no big cameras using them when DECam was planned, they had to decide to take a risk.”

A zoomed-in image from the Dark Energy Camera of the barred spiral galaxy NGC 1365, in the Fornax cluster of galaxies, which lies about 60 million light-years from Earth.

The DECam chips were fabricated by Berkeley Lab’s industrial partner, Teledyne Dalsa Semiconductor, and the Physics Div.’s MicroSystems Laboratory. Partially finished wafers holding four CCDs, each with eight of 11 masking steps completed, were commercially thinned, then sent to the MicroSystems Laboratory for completion. “Cold probe” tests at -45 °C were performed to detect shorts, defects and excessive dark current. The CCDs were cut from the wafer and sent to Fermilab for mounting and final testing of the science-grade devices.

The survey is expected to begin this month, after the camera is fully tested, and will take advantage of the excellent atmospheric conditions in the Chilean Andes to deliver pictures with the sharpest resolution seen in such a wide-field astronomy survey. In just its first few nights of testing, the camera has delivered images with excellent and nearly uniform spatial resolution, astronomers say.

Over five years, the survey will create detailed color images of one-eighth of the sky, or 5000 square degrees, to discover and measure 300 million galaxies, 100,000 galaxy clusters and 4000 supernovae.

The scientific observation of celestial radiation that has reached the vicinity of Earth, and the interpretation of these observations to determine the characteristics of the extraterrestrial bodies and phenomena that have emitted the radiation.
The displacement of spectrum lines, as determined by the increasing distance between, and the relative velocity of, the observer and a light source, causing the lines to move toward the red portion of the spectrum. It is used in astrophysics to determine the rate of recession or expansion of celestial bodies. Also known as the Hubble effect.
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