Recent observations have validated astronomers’ predictions that quasars from the early Universe emerged in regions abundant with companion galaxies. The Dark Energy Camera (DECam) was instrumental in achieving this conclusion, providing a wide field of view and specialized filters that helped clarify why previous research aimed at understanding the density of quasar surroundings produced mixed results.
Quasars are the brightest entities in the Universe, fueled by material that is drawn into supermassive black holes located at the centers of galaxies. Research indicates that the black holes in early-Universe quasars are so enormous that they must have been consuming gas at incredibly high rates. This leads most scientists to believe that these quasars originated in some of the Universe’s most densely populated regions, where gas was plentiful. Nevertheless, observational data attempting to verify this notion have yielded inconsistent outcomes. A new study using the Dark Energy Camera (DECam) provides insights into these conflicting findings and builds a logical connection between observation and theory.
DECam, developed by the Department of Energy, is mounted on the VÃctor M. Blanco 4-meter Telescope at the Cerro Tololo Inter-American Observatory in Chile, a program of NSF NOIRLab.
The research was headed by Trystan Lambert, who conducted this study as a PhD student at the Institute of Astrophysical Studies of Diego Portales University in Chile and is now a postdoctoral researcher at the University of Western Australia’s node of the International Centre for Radio Astronomy Research (ICRAR). With DECam’s expansive field of view, the team undertook the largest ever sky search for an early-Universe quasar to assess its surrounding environment by counting nearby companion galaxies.
For this study, the team required a quasar with a precisely determined distance. They were fortunate to select quasar VIK J2348-3054, which has a known distance established by earlier observations with the Atacama Large Millimeter/submillimeter Array (ALMA). DECam’s three-square-degree field of view allowed for a broad examination of its cosmic environment. Additionally, DECam includes a specialized narrowband filter designed for detecting companion galaxies. “This quasar study was truly a perfect opportunity,” Lambert explains. “We had a quasar with a well-established distance, and DECam on the Blanco telescope provided the large field of view and specific filter we needed.”
Thanks to DECam’s specialized filter, the team could count the companion galaxies near the quasar by identifying a particular type of light they emit, known as Lyman-alpha radiation. This radiation is a characteristic energy signature of hydrogen, produced when hydrogen is ionized and then recombines during star formation. Lyman-alpha emitters typically belong to younger, smaller galaxies, and their emissions can reliably indicate their distances. By measuring the distances of multiple Lyman-alpha emitters, researchers can create a 3D map of a quasar’s surroundings.
After meticulously mapping the space around quasar VIK J2348-3054, Lambert and his team identified 38 companion galaxies within a distance of 60 million light-years, aligning with expectations for quasars in dense regions. However, they were taken aback to discover that there were no companion galaxies within 15 million light-years of the quasar.
This observation sheds light on the results of previous studies aimed at categorizing early-Universe quasar environments and offers a potential explanation for the contradicting outcomes observed before. No other research of this kind has utilized a search area as expansive as DECam’s, so smaller surveys may present a quasar’s environment as misleadingly empty.
“DECam’s extensive field of view is essential for comprehensively studying quasar neighborhoods. It’s necessary to examine a larger expanse,” Lambert remarks. “This offers a rational explanation for the discrepancies in earlier observations.”
The team posits that the absence of companion galaxies in the immediate vicinity of the quasar may be due to the intense radiation emitted by the quasar, which could inhibit star formation in these nearby galaxies, rendering them invisible from our observations.
“Some quasars are anything but quiet neighbors,” Lambert points out. “Stars in galaxies form from gas that requires a cold enough temperature to collapse under its own gravity. Bright quasars can potentially heat this gas in nearby galaxies, preventing it from collapsing and forming stars.”
Lambert’s team is currently conducting further observations to gather spectral data and verify the suppression of star formation. They also plan to study additional quasars to create a more comprehensive dataset.
“These findings highlight the importance of the strong collaboration between the National Science Foundation and the Department of Energy,” states Chris Davis, NSF program director for NSF NOIRLab. “We anticipate significant advancements with the forthcoming NSF-DOE Vera C. Rubin Observatory, a next-generation facility that will uncover even more about the early Universe and these extraordinary objects.”
Notes
[1] This research was facilitated through a partnership between researchers at Diego Portales University and the Max Planck Institute of Astronomy. A portion of this project was supported by a grant from Chile’s National Research and Development Agency (ANID) for collaborations with the Max Planck Institutes.
