First discovery of a pair of merging quasars in the cosmic dawn

First discovery of a pair of merging quasars in the cosmic dawn
First discovery of a pair of merging quasars in the cosmic dawn

With the help of the Gemini North telescope, a team of astronomers has discovered a pair of merging quasars seen just 900 million years ago 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 in the history of the Universe known as Cosmic Dawn.

The Cosmic Dawn extended 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. The arrival of the first stars and galaxies began a new era in the formation of the cosmos known as the Epoch of Reionization.

The Epoch of Reionization, which took place 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 spread throughout the cosmos, interacting with the intergalactic medium and stripping the Universe’s primordial hydrogen atoms of their electrons in a known process. like ionization. The Epoch of Reionization was a critical epoch in the history of the Universe that marked the end of the cosmic dark ages and seeded the large structures we observe today in our local Universe.

To understand the exact role quasars played during the epoch of reionization, astronomers are interested in finding and studying the quasars that populated this early, distant era. “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 the Cosmic Dawn, and the earliest evolution of quasar host galaxies. “, highlights Yoshiki Matsuok, astronomer at Ehime University in Japan and lead author of the article describing these results, published in ‘Astrophysical Journal Letters’.

About 300 quasars have been discovered in the Reionization Epoch, but none of them have been found in pairs. That was until Matsuoka and his team were reviewing images taken with the Hyper Suprime-Cam on the Subaru Telescope and a faint red spot caught their attention. “While examining images of quasar candidates, I noticed two similar, extremely red sources, side by side,” says Matsuoka. “The discovery was purely fortuitous.”

The team wasn’t sure they were a pair of quasars, since distant quasar candidates are contaminated by many 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. Spectra obtained with GNIRS, which decompose the light emitted by a source into its component wavelengths, were crucial in characterizing the nature of the quasar pair and their host galaxies.

“What we learned from the GNIRS observations was that quasars are too faint to detect in the near-infrared, even with one of the largest ground-based telescopes,” notes 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 enormous, each having 100 million times the mass of the Sun. This, along with the presence of a gas bridge spanning between the two quasars, suggests that they and Their host galaxies are undergoing a large-scale merger.

“The existence of merging quasars in the Reionization Epoch has been anticipated for a long time. Now it has been confirmed for the first time,” says Matsuoka.

The Epoch of Reionization connects the earliest formation of cosmic structure with the complex Universe we observe billions of years later. By studying distant objects from this period, astronomers gain valuable information about the reionization process and the formation of the first objects in the Universe. More discoveries like this may be on the horizon with the NSF-DOE Vera C. Rubin Observatory’s decade-long Legacy Survey of Space and Time (LSST), starting in 2025, set to detect millions of quasars. using its deep imaging capabilities.

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