Astronomers discover the very first pair of merging quasars at Cosmic Dawn

Astronomers discover the most distant pair of merging quasars, seen only 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 insights into the formation of supermassive black holes and the early evolution of galaxies, highlighting an important cosmological transition during the epoch of reionization.

Cosmic expansion and quasar formation

Since the very first moment after the Big Bang, the universe has been expanding. This means that the early universe was significantly smaller and early-formed galaxies were more likely to interact and merge. The merger of galaxies stimulates the formation of quasars – extremely luminous galaxy cores in which gas and dust falling into a central supermassive black hole emit enormous amounts of light. So looking back to the early universe, astronomers would expect to find countless pairs of quasars close together as their host galaxies merged. However, they were surprised to find exactly none so far.

A team of astronomers has discovered a double-record-breaking pair of quasars. They are not only the most distant pair of merging quasars ever found, but also the only pair confirmed in the distant era of the universe’s earliest formation.

Discovery of distant merging quasars

Using the Gemini North telescope, half of the International Gemini Observatory, which is supported in part by the U.S. National Science Foundation and operated by NSF NOIRLaba team of astronomers has discovered a pair of merging quasars that occurred just 900 million years after the Big bang. This is not only the most distant pair of merging quasars ever found, but also the first confirmed pair in the period of the universe’s history known as Cosmic Dawn.

The meaning of cosmic dawn and reionization

Cosmic Dawn lasted from about 50 million years to a 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. With the arrival of the first stars and galaxies, a new era in the formation of the cosmos began, known as the era of reionization.

The age of reionization, which occurred within the Cosmic Dawn, was a period of cosmological transition. About 400 million years after the Big Bang, ultraviolet light from the first stars, galaxies and quasars began to spread through the cosmos, interacting with the intergalactic medium and stripping the primordial hydrogen atoms of the universe of their electrons in a process called is known as ionization. The Age of Reionization was a pivotal era in the history of the Universe that marked the end of the cosmic Dark Ages and formed the basis for the large structures we observe in our local Universe today.

Quasars and the Age of Reionization

To understand the exact role quasars played during the epoch of reionization, astronomers are interested in finding and studying quasars that populate this early and distant epoch.

“The statistical properties of quasars in the epoch of reionization tell us many things, such as the progress and origin of reionization, the formation of supermassive black holes during Cosmic Dawn, and the earliest evolution of the quasar hosts,” says Yoshiki Matsuoka. , an astronomer at Ehime University in Japan and lead author of the paper describing these results, published in the Astrophysical diary letters.

Revealing the Quasar pair

About 300 quasars have been discovered in the Age of Reionization, but none have been found in a few. That is until Matsuoka and their team were looking at images taken with the Hyper Suprime-Cam on the Subaru Telescope and a faint red spot caught their attention. “While screening images of quasar candidates, I saw two similar and extremely red sources next to each other,” says Matsuoka. “The discovery was purely coincidental.”

The team wasn’t sure they were a quasar pair because distant quasar candidates are contaminated by numerous other sources, such as foreground stars and galaxies and the effects of gravitational lensing. To confirm the nature of these objects, the team performed follow-up spectroscopy using the Faint Object Camera and Spectrograph (FOCAS) on the Subaru Telescope and the Gemini Near-Infrared Spectrograph (GNIRS) on Gemini North. The spectra obtained with GNIRS, which split the emitted light from a source into its component wavelengths, were crucial for characterizing the nature of the quasar pair and their host galaxies.

Implications of the discovery

“What we learned from the GNIRS observations is that the quasars are too faint to detect in the near-infrared, even with one of the largest ground-based telescopes,” says Matsuoka. 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 discovered that the two black holes are big ones, each with 100 million times the mass of the Sun. This, combined 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 epoch of reionization has long been expected. It has now been confirmed for the first time,” said Matsuoka.^[2]

Future prospects in Quasar research

The epoch of reionization links 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 with NSF-DOE Vera C. Rubin Observatory’s decade-long Legacy Survey of Space and Time (LSST), which begins in 2025 and is poised to explore millions of quasars detect using its deep imaging capabilities.

Comments

1. 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 made with the Atacama Large Millimeter/submillimeter Array (ALMA).
2. There have been candidates, but it is difficult to separate them from possible gravitational images of a single quasar. There are also some candidates to be doubly active galactic nuclei, embedded in individual galaxies from the epoch of reionization, but these have much lower luminosities (black hole activity) than quasars and are two components within a single galaxy, which are qualitatively different from what is described here.

Reference: “Discovery of Merging Twin Quasars at z = 6.05” by Yoshiki Matsuoka, Takuma Izumi, Masafusa Onoue, Michael A. Strauss, Kazushi Iwasawa, Nobunari Kashikawa, Masayuki Akiyama, Kentaro Aoki, Junya Arita, Masatoshi Imanishi, Rikako Ishimoto, Toshihiro Kawaguchi, Kotaro Kohno, Chien-Hsiu Lee, Tohru Nagao, John D. Silverman and Yoshiki Toba, April 5, 2024, The astrophysical diary 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 of Tokyo, Japan), Masatoshi Imanishi (National Astronomical Observatory of Japan, Graduate University for Advanced Studies [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)