Dark Energy Camera

Dark Energy Camera. It is a high-performance, wide-field imaging instrument specifically designed for the Dark Energy Survey, a major international cosmology project. Mounted on the Víctor M. Blanco Telescope at the Cerro Tololo Inter-American Observatory in Chile, its primary mission is to map hundreds of millions of galaxies to investigate the nature of dark energy. The camera's unprecedented sensitivity and large field of view have made it one of the premier survey instruments in the world, contributing to numerous discoveries in astrophysics and cosmology.

Overview

The instrument was conceived and built by a collaboration involving the U.S. Department of Energy, the National Science Foundation, and institutions like Fermilab and the University of Chicago. Its installation marked a significant upgrade to the capabilities of the Víctor M. Blanco Telescope, which is operated by the Association of Universities for Research in Astronomy. Since achieving first light in 2012, it has been the workhorse instrument for the Dark Energy Survey, which completed its primary observations in 2019. The data collected has been instrumental in producing detailed maps of the large-scale structure of the universe and measuring the accelerating expansion driven by dark energy.

Design and construction

The camera's design centers on a array of sixty-two fully depleted charge-coupled device sensors, developed in partnership with Lawrence Berkeley National Laboratory. This massive focal plane, spanning over half a meter in diameter, provides a field of view of 2.2 square degrees, allowing it to capture vast swaths of the southern celestial hemisphere in a single exposure. A complex five-element optical corrector, featuring lenses up to a meter in diameter, was engineered to deliver sharp images across this wide field. Major construction and assembly took place at Fermilab, with final integration and commissioning occurring at Cerro Tololo Inter-American Observatory.

Scientific objectives and discoveries

The primary objective was to constrain the properties of dark energy by measuring its effect on the history of cosmic expansion and the growth of structure. This was pursued through four complementary techniques: studying Type Ia supernovae, measuring baryon acoustic oscillations, analyzing the weak gravitational lensing of galaxies, and counting galaxy clusters. Key discoveries include some of the most precise measurements of cosmological parameters, detailed dark matter maps via weak gravitational lensing, and the discovery of numerous distant trans-Neptunian objects and supernovae. The data has also fueled studies on Milky Way structure, quasars, and gamma-ray bursts.

Technical specifications

The camera's focal plane contains 570 megapixels across its sixty-two science charge-coupled devices. It operates across the optical and near-infrared spectrum using a set of five filters (g, r, i, z, Y) defined by the Sloan Digital Sky Survey system. The entire instrument, including its cryogenic cooling system for the sensors, weighs approximately four tons. It achieves a remarkable image quality, with a typical point spread function of less than 0.9 arcseconds, which is critical for precise shape measurements for weak gravitational lensing analyses.

Operations and data management

Operations are conducted remotely by teams from the Dark Energy Survey collaboration, with support from staff at Cerro Tololo Inter-American Observatory. A typical observing night produces up to 200 gigabytes of raw data, which is transferred via high-speed networks to processing centers at the National Center for Supercomputing Applications and Fermilab. The data processing pipeline, known as the Dark Energy Survey Data Management system, calibrates images, detects astronomical sources, and produces catalogs used by hundreds of scientists worldwide. After the conclusion of the Dark Energy Survey, the camera continues to be used for other scientific programs under the DECam Legacy Survey and by the general astronomical community.