The Dark Energy Survey

The Dark Energy Survey

Simulated image of the DECam CCD array at focal plane. Each large rectangle is a single CCD. The green rectangle in upper left corner represents the size of the iPhone 4 CCD relative to DECam CCDs
Alternative names	DES
Survey type	astronomical survey
Target	dark energy
Observations	Cerro Tololo Inter-American Observatory
Website	www.darkenergysurvey.org
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The Dark Energy Survey (DES) is an optical and near-infrared survey that aims to probe the dynamics of the expansion of the Universe and the growth of large-scale structure. The collaboration is composed of research institutions and universities from the United States, Brazil, the United Kingdom, Germany, Spain, and Switzerland.

The survey uses the 4-meter Victor M. Blanco Telescope located at Cerro Tololo Inter-American Observatory (CTIO) in Chile, outfitted with the Dark Energy Camera (DECam). This camera allows for more sensitive images in the red part of the visible spectrum and in the near infrared, in comparison to previous instruments.

DECam has one of the widest fields of view (2.2-degree diameter) available for ground-based optical and infrared imaging. The survey will image 5,000 square degrees of the southern sky in a footprint that overlaps with the South Pole Telescope and Stripe 82 (in large part avoiding the Milky Way). The survey will take five years to complete, and the survey footprint will nominally be covered ten times in five photometric bands (g, r, i, z, and Y). DES officially began in August 2013 and completed its second season in February 2015.

The Dark Energy Survey investigates the dynamics and large scale structure of the Universe using four probes: Type Ia supernovae, baryon acoustic oscillations (BAO), the number of galaxy clusters, and weak gravitational lensing.

Type Ia supernovae are believed to be thermonuclear explosions that occur when white dwarf stars in binary systems accrete mass from their companion stars. These events are important for the study of cosmology because they are very bright, which allows astronomers to detect them at very large distance. The expansion of the universe can be constrained based on observations of the luminosity distance and redshift of distant type IA supernova. The other three techniques (BAO, galaxy clusters, and weak lensing) used by the Dark Energy Survey allow scientists to understand simultaneously the expansion of the universe and the evolution of the dark matter density field perturbations. These perturbations were intrinsically tied to the formation of galaxies and galaxy clusters. The standard model of cosmology assumes that quantum fluctuations of the density field of the various components that were present when our universe was very young were enhanced through a very rapid expansion called inflation. Gravitational collapse enhances these initial fluctuation as baryons fall into the gravitational potential field of more dense regions of space to form galaxies. Nevertheless, the growth rate of these dark matter halos is sensitive to the dynamics of the expansion of the Universe and DES will use this connection to probe the properties of that expansion.