An article published in the journal “The Astrophysical Journal Letters” reports the discovery of the most distant pair of merging quasars known. A team of researchers combined observations from the Subaru Telescope with the Gemini North Telescope to find traces of this pair of quasars that we see as they were about 900 million years after the Big Bang.
The top image (NOIRLab/NSF/AURA/T.A. Rector (University of Alaska Anchorage/NSF NOIRLab), D. de Martin (NSF NOIRLab) & M. Zamani (NSF NOIRLab)) shows the pair of quasars photographed by the Hyper Suprime-Cam mounted on Subaru Telescope.
Studying this pair of quasars can offer new insights into the epoch of reionization, the period that began about 400 million years after the Big Bang and was crucial in the history of the universe. That’s the time when the neutral, light-blocking hydrogen was ionized, resulting in the universe becoming the bright place we know today. An article accepted for publication in a journal of the American Astronomical Society offers further analysis based on observations conducted with the ALMA radio telescope.
Quasars are the brightest objects in the universe thanks to the electromagnetic emissions generated by materials orbiting a supermassive black hole. Their role in the reionization is still being studied and is why the search for primordial quasars is important.
About 300 quasars dating back to the reionization era are known but no pairs. However, when the authors of this new study examined images captured by the Hyper Suprime-Cam mounted on the Subaru Telescope as part of the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project, they noticed two light sources that were similar and near each other, cataloged as HSC J121503.42−014858.7 (C1) and HSC J121503.55−014859.3 (C2).
To understand if the two objects discovered were indeed a pair of quasars, the researchers conducted follow-up observations. The Faint Object Camera and Spectrograph (FOCAS) instrument, also mounted on the Subaru Telescope, made it possible to obtain a spectroscopic exam of the objects. A second exam was conducted using the Gemini Near-Infrared Spectrograph (GNIRS) instrument mounted on the Gemini North Telescope.
These exams made it possible to understand that part of the light detected at optical frequencies didn’t come from the quasars but from the stars that are forming in the galaxies that host them. The data obtained on the supermassive black holes that power the quasars suggest that their masses are truly remarkable considering their age, being in both cases around 100 million times the Sun’s.
A further discovery obtained is a sort of gas bridge across the two galaxies that host the quasars. This not only proves that it’s a pair but indicates that the two galaxies are in the process of merging. This is the first known pair of quasars dating back to what is called the Cosmic Dawn, the period between about 50 million years and a billion years after the Big Bang.
Astronomers assumed that there had been mergers between galaxies hosting quasars during the epoch of reionization because galaxy mergers are common events. The problem is in observing events so distant in space and time and only now has success arrived. Studying these quasars will help reconstruct that crucial phase in the history of the universe. It’s the reason why searches for mergers between primordial quasars continue and in the future will also be conducted with new instruments that will come into service.
