Sep 23

DECam Confirms that Early-Universe Quasar Neighborhoods are Indeed Cluttered

Artist Illustration of Early-Universe Quasar Cosmic Neighborhood. Bright white star in a filed of black dotted with stars and galaxies.
Artist Illustration of Early-Universe Quasar Cosmic Neighborhood Credit: NOIRLab/NSF/AURA/M. Garlick/J. da Silva (Spaceengine)/M. Zamani

Observations using the Dark Energy Camera (DECam) confirm astronomers’ expectation that early-Universe quasars formed in regions of space densely populated with companion galaxies. DECam’s exceptionally wide field of view and special filters played a crucial role in reaching this conclusion, and the observations reveal why previous studies seeking to characterize the density of early-Universe quasar neighborhoods have yielded conflicting results.

Quasars are the most luminous objects in the Universe and are powered by material accreting onto supermassive black holes at the centers of galaxies. Studies have shown that early-Universe quasars have black holes so massive that they must have been swallowing gas at very high rates, leading most astronomers to believe that these quasars formed in some of the densest environments in the Universe where gas was most available. However, observational measurements seeking to confirm this conclusion have thus far yielded conflicting results. Now, a new study using the Dark Energy Camera (DECam) points the way to both an explanation for these disparate observations and also a logical framework to connect observation with theory.

DECam was fabricated by the Department of Energy and is mounted on the U.S. National Science Foundation Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory in Chile, a Program of NSF NOIRLab.

The study was led by Trystan Lambert, who completed this work as a PhD student at Diego Portales University’s Institute of Astrophysical Studies in Chile [1] and is now a postdoc at the University of Western Australia node at the International Centre for Radio Astronomy Research (ICRAR). Utilizing DECam’s massive field of view, the team conducted the largest on-sky area search ever around an early-Universe quasar in an effort to measure the density of its environment by counting the number of surrounding companion galaxies.

For their investigation, the team needed a quasar with a well-defined distance. Luckily, quasar VIK 2348–3054 has a known distance, determined by previous observations with the Atacama Large Millimeter/submillimeter Array (ALMA), and DECam’s three-square-degree field of view provided an expansive look at its cosmic neighborhood. Serendipitously, DECam is also equipped with a narrowband filter perfectly matched for detecting its companion galaxies. “This quasar study really was the perfect storm,” says Lambert. “We had a quasar with a well-known distance, and DECam on the Blanco telescope offered the massive field of view and exact filter that we needed.”

Read more on the NOIRLab website