This image shows two quasars in the process of merging. Using the Gemini North telescope, one half of the Gemini International Observatory supported in part by the US National Science Foundation and operated by the NSF NOIRLab, and the Subaru telescope, a team of astronomers discovered a pair of merging quasars that were only seen 900 million years after the big bang. Not only is this the most distant pair of merging quasars ever found, it is also the first confirmed pair found in the period of space known as the Cosmic Dawn. Credit: International Gemini Observatory/NOIRLab/NSF/AURA/M. Garlic
Astronomers discover the most distant pair of merging quasars ever seen just 900 million years after the Big Bang.
This period, known as the Cosmic Dawn, is crucial because it marks the beginning of the formation of stars and galaxies that led to the reionization of the universe. These quasars provide insight into the formation of supermassive black holes and the early evolution of galaxies, highlighting a major cosmological transition during the epoch of reionization.
Cosmic expansion and quasar formation
From the first moment after the big bang, the universe has been expanding. This means that the early universe was significantly smaller and the early formed galaxies were more likely to interact and merge. The merging of galaxies triggers the formation of quasars – extremely luminous galactic nuclei, where gas and dust collapsing into a central supermassive black hole emit enormous amounts of light. So, looking back at the early universe, astronomers would expect to find many pairs of quasars in close proximity to each other as their host galaxies undergo mergers. However, they were surprised to find exactly none – until now.
A team of astronomers discovered a pair of quasars that broke two records. Not only are they the most distant pair of merging quasars ever found, they are also the only pair confirmed in the past era of the earliest formation of the universe.
Discovery of distant merging quasars
With the help of the Gemini North telescope, half of the Gemini International Observatory was created, which is supported in part by the US National Science Foundation and operated by the NSF NOIRLabA team of astronomers has discovered a pair of merging quasars observed only 900 million years after Big Bang. Not only is this the most distant pair of merging quasars ever found, it is also the first confirmed pair in the period of cosmic history known as the Cosmic Dawn.
The meaning of cosmic dawn and reionization
The Cosmic Dawn lasted from about 50 million years to one billion years after the Big Bang. During this period, the first stars and galaxies began to appear, filling the dark universe with light for the first time. The arrival of the first stars and galaxies started a new era in the formation of the cosmos known as the epoch of reionization.
Although we are not sure exactly when the first stars began to shine, we do know that they must have formed sometime after the recombination era when hydrogen and helium atoms formed (380,000 years after the Big Bang) and before the oldest known galaxies. existed (400 million years after the big bang). The ultraviolet light emitted by the first stars broke the neutral hydrogen gas filling the universe into hydrogen ions and free electrons, ushering in the era of reionization and the end of the dark ages of the universe. Credit: NASA, ESA, CSA, STScI
The epoch of reionization that took place as part of the Cosmic Dawn was a time of cosmological transition. Beginning roughly 400 million years after the Big Bang, ultraviolet light from the first stars, galaxies, and quasars traveled through space, interacting with the intergalactic medium and stripping the universe’s primordial hydrogen atoms of their electrons in a process known as ionization. The epoch of reionization was a critical epoch in the history of the universe, marking the end of the cosmic dark ages and establishing the large structures we observe today in our local universe.
Quasars and the epoch of reionization
To understand the exact role that quasars played during the epoch of reionization, astronomers are interested in finding and studying quasars that inhabit this early and distant period.
“The statistical properties of quasars in the reionization epoch tell us many things, such as the progress and origin of reionization, the formation of supermassive black holes during the Cosmic Dawn, and the earliest evolution of quasar host galaxies,” said Yoshiki Matsuoka. , an astronomer at Ehime University in Japan and lead author of a paper describing these results, published in Astrophysical Journal Letters.
This image taken with the Subaru Telescope’s Hyper Suprime-Cam shows a pair of quasars in the process of merging. The faint red spots caught the attention of astronomers, and subsequent spectroscopy with the Gemini North telescope, one half of the Gemini International Observatory, which is supported in part by the US National Science Foundation and operated by the NSF NOIRLab, confirmed that the objects were quasars. The pair is only seen 900 million years after the big bang. Not only is this the most distant pair of merging quasars ever found, it is also the first confirmed pair in the period of cosmic history known as the Cosmic Dawn. Credit: NOIRLab/NSF/AURA/TA Rector (University of Alaska Anchorage/NSF NOIRLab), D. de Martin (NSF NOIRLab) & M. Zamani (NSF NOIRLab)
Quasar Pair Revealed
About 300 quasars have been discovered in the reionization epoch, but none of them have been found in a pair. That is, until Matsuoka and his team were viewing images taken with the Hyper Suprime-Cam on the Subaru telescope and a faint red spot caught their eye. “While examining images of quasar candidates, I noticed two similar and extremely red sources next to each other,” Matsuoka said. “The discovery was purely accidental.”
The team was not sure it was a quasar pair because distant quasar candidates are contaminated by a variety of other sources, such as foreground stars and galaxies and gravitational lensing effects. To confirm the nature of these objects, the team performed follow-up spectroscopy using the Camera and Spectrograph for Faint Objects (FOCAS) on the Subaru Telescope and the Gemini Near Infrared Spectrograph (GNIRS) on Gemini North. The spectra, which decompose the light emitted from the source into its sub-wavelengths, obtained with GNIRS, were essential for characterizing the nature of the quasar pair and their host galaxies.
Implications of the discovery
“From the GNIRS observations, we learned that quasars are too faint to be detected in the near-infrared region, even with one of the largest telescopes on earth,” Matsuoka said. This allowed the team to estimate that some of the light detected in the optical wavelength range does not come from the quasars themselves, but from the ongoing star formation taking place in their host galaxies. The team also found that both black holes are enormous, each 100 million times the size of the Sun. This, along with the presence of a gas bridge stretching between the two quasars, suggests that they and their host galaxies are undergoing a large-scale merger.[1]
“The existence of merging quasars in the reionization epoch has been expected for a long time. Now it has been confirmed for the first time,” Matsuoka said.[2]
Future prospects in quasar research
The epoch of reionization connects the earliest formation of cosmic structure to the complex universe we observe billions of years later. By studying distant objects from this period, astronomers gain valuable insight into the process of reionization and the formation of the first objects in the universe. More such discoveries may be on the horizon thanks to the NSF–DOE Vera C. Rubin Observatory’s 10-year Legacy Survey of Space and Time (LSST), starting in 2025, which is poised to detect millions of quasars with its deep imaging capabilities.
Comment
- A companion paper accepted for publication in AAS Journals presents further analysis of the quasar pair, the gas bridge between them, and their host galaxies using observations taken with the Atacama Large Millimeter/submillimeter Array (ALMA).
- Candidates have existed, but are difficult to separate from possibly gravitationally lensed images of a single quasar. There are also some candidates for dual active galactic nuclei embedded in individual epochs of reionizing galaxies, but these are of much lower luminosity (Black hole activity) than quasars and are two components within a single galaxy that are qualitatively different from what is described here.
Reference: “Discovery of double quasar mergers at z = 6.05” by Yoshiki Matsuoka, Takuma Izumi, Masafusa Onoue, Michael A. Strauss, Kazushi Iwasawa, Nobunari Kashikawa, Masayuki Akiyama, Kentaro Aoki, Junya Tomanishio, Rika Ishimo, Masato Ishito Kawaguchi , Kotaro Kohno, Chien-Hsiu Lee, Tohru Nagao, John D. Silverman, and Yoshiki Toba, 5 Apr 2024, The Astrophysical Journal Letters.
DOI: 10.3847/2041-8213/ad35c7
The team consists of Yoshiki Matsuoka (Ehime University, Japan), Takuma Izumi (National Astronomical Observatory of Japan, Tokyo), Masafusa Onoue (Kavli Institute for the Physics and Mathematics of the Universe, Japan), Michael A. Strauss (Princeton UniversityUSA), Kazushi Iwasawa (Universitat de Barcelona Spain), Nobunari Kashikawa (University of Tokyo, Japan), Masayuki Akiyama (Tohoku University, Japan), Kentaro Aoki (Subaru Telescope, National Astronomical Observatory of Japan, USA), Junya Arita (University in Tokyo, Japan), Masatoshi Imanishi (National Astronomical Observatory of Japan, Graduate University for Advanced Study [SOKENDAI]Japan), Rikako Ishimoto (University of Tokyo, Japan), Toshihiro Kawaguchi (Onomichi City University, Japan), Kotaro Kohno (University of Tokyo, Japan), Chien-Hsiu Lee (WM Keck Observatory, USA), Tohru Nagao (Ehime University , Japan), John D. Silverman (Kavli Institute for the Physics and Mathematics of the Universe, Japan) and Yoshiki Toba (Ehime University, Japan, National Astronomical Observatory of Japan, Tokyo, Academia Sinica Institute of Astronomy and Astrophysics, Taiwan )