Using the Atacama Large Millimeter/submillimeter Array (ALMA) and the Subaru Telescope, astronomers have discovered a pair of merging gas-rich galaxies that existed 12.8 billion years ago. These galaxies, hosting faint quasars at their centers, could be the ancestors of the brightest and most massive quasars in the early Universe.
An artist’s impression of HSC J121503.42-014858.7 and HSC J121503.55-014859.3 quasars. Image credit: Izumi et al., doi: 10.3847/1538-4357/ad57c6.
Quasars are bright objects powered by matter falling into a supermassive black hole at the center of a galaxy in the early Universe.
The most accepted theory is that when two gas-rich galaxies merge to form a single larger galaxy, the gravitational interaction of the two galaxies causes gas to fall towards the supermassive black hole in one or both of the galaxies, causing quasar activity.
To test this theory, Dr. Takuma Izumi from the National Astronomical Observatory of Japan used ALMA to study the earliest known pair of close quasars.
Labeled HSC J121503.42-014858.7 and HSC J121503.55-014859.3, these quasars were discovered by the Hyper Suprime-Cam on the Subaru Telescope.
These objects are very faint — about 10 to 100 times fainter than high-luminosity quasars at the same redshift.
“Located approximately 12.8 billion light-years away, corresponding to the ‘Cosmic Dawn’ era when the Universe was only 900 million years old, this is the most distant record of such pair of quasars,” the astronomers said.
“Due to their faintness, we thought these objects were in the pre-merger stage before the rapid growth of the supermassive black holes.”
“However, observations with the Subaru Telescope could only provide information about the central supermassive black holes, leaving unanswered whether the host galaxies were destined to merge and eventually grow into high-luminosity quasars.”
“As a next step, we conducted observations of the host galaxies of these pair quasars using the ALMA radio telescope.”
“The results were astonishing: the distribution of interstellar matter observed and the nature of their motion indicated that these galaxies were interacting.”
“They are undoubtedly on the path to merging into a single galaxy shortly.”
“Furthermore, calculations from the observational data revealed that the total gas mass in these galaxies (around 100 billion times the mass of the Sun) is comparable to or even more significant than the gas masses of the host galaxies of most high-luminosity quasars, whose nuclei are extraordinarily bright.”
“With this tremendous amount of material, post-merger explosive star formation and fueling of the supermassive black holes should be easily triggered and sustained.”
“Therefore, these findings represent a significant achievement in identifying the ancestors of high-luminosity quasars — the brightest celestial objects in the early Universe — and starburst galaxies from multiple perspectives, including galaxy structure, motion, and the amount of interstellar matter.”
The findings appear in the Astrophysical Journal.
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Takuma Izumi et al. 2024. Merging Gas-rich Galaxies That Harbor Low-luminosity Twin Quasars at z=6.05: A Promising Progenitor of the Most Luminous Quasars. ApJ 972, 116; doi: 10.3847/1538-4357/ad57c6