Camera Detects 23 Clues to Cosmic Dawn

The Dark Energy Camera (DECam) has detected 23 young galaxies, seen as they were 800 million years after the Big Bang occurred. DECam was recently made even more powerful when it was equipped with a special narrowband filter, designed by researchers at Arizona State University (ASU).

Milestones in the history of the universe (not to scale). The intergalactic gas was in a neutral state from about 300,000 years after the Big Bang until light from the first generation of stars and galaxies began to ionize it. The gas was completely ionized after 1 billion years. The Lyman Alpha Galaxies in the Epoch of Reionization (LAGER) study takes a close look at the state of the universe at 800 million years (yellow box) to investigate when and how this transformation occurred. Courtesy of National Astronomical Observatory of Japan.

The galaxy search using the ASU-designed filter and DECam is the largest uniformly selected sample that goes far enough back in the history of the universe to reach cosmic dawn, the point in time when the first stars and galaxies appeared, illuminating and transforming the universe.

“Several years ago, we carried out a similar study using a 64-megapixel camera that covers the same amount of sky as the full moon," said astronomer James Rhoads. “DECam, by comparison, is a 570-megapixel camera and covers 15 times the area of the full moon in a single image.”

The research team spent several months refining the design of the filter profile, optimizing the filter to achieve maximum sensitivity.

Roberto Tighe and Nicole David checking filter N964 following installation into its mounting frame in the Blanco cleanroom. Courtesy of NOAO Newsletter issue 113, Freddy Muñoz/NOAO/AURA/NSF.

“The combination of large survey size and sensitivity of this survey enables us to study galaxies that are common but faint, as well as those that are bright but rare, at this early stage in the universe,” said astronomer Sangeeta Malhotra.

The DECam is installed at the National Optical Astronomy Observatory (NOAO)’s four-meter Blanco Telescope, located at the Cerro Tololo Inter-American Observatory (CTIO) in northern Chile, at an altitude of 7200 feet.

False color image of a 2-square-degree region of the LAGER survey field, created from images taken in the optical at 500 nm (blue), in the NIR at 920 nm (red), and in a narrow-band filter centered at 964 nm (green). The small white boxes indicate the positions of the 23 Lyman-alpha emitters (LAEs) discovered in the survey. The detailed insets (yellow) show two of the brightest LAEs. Courtesy of Zhenya Zheng (SHAO) & Junxian Wang (USTC).

“Our findings in this survey imply that a large fraction of the first galaxies that ionized and illuminated the universe formed early, less than 800 million years after the Big Bang,” said astronomer Junxian Wang.

Building on these results, the team plans to continue to search for star-forming galaxies over a larger volume of the universe and to further investigate the nature of some of the first galaxies in the universe.

The research was published in The Astrophysical Journal Letters (doi: 10.3847/2041-8213/aa794f).