In 2019, a study using Hyper Suprime-Cam (HSC) on the Subaru Telescope reported the discovery of a large number of supermassive black holes (SMBHs) in the early Universe, from an epoch when the Universe was less than 10 percent of its present age (Note 1). At that time, the research team expressed their hope that subsequent follow-up observations would provide new insights into the formation and evolution of SMBHs in the early Universe. Now, observations of one of the galaxies containing a SMBH with the Atacama Large Millimeter/submillimeter Array (ALMA) revealed a titanic "galactic wind" driven by the SMBH.
At the center of many large galaxies hides a SMBH that is millions to billions of times more massive than the Sun. Interestingly, the mass of the black hole is roughly proportional to the mass of the central region (bulge) of the galaxy in the present-day Universe. At first glance, this may seem obvious, but it is actually very strange, because the sizes of galaxies and black holes differ by about 10 orders of magnitude. Based on this proportional relationship between the masses of two objects that are so different in size, astronomers believe that galaxies and black holes grew and evolved together (coevolution) through some kind of physical interaction.
A galactic wind can provide this kind of physical interaction between SMBHs and galaxies. A SMBH swallows a large amount of matter. As that matter begins to move at high speed due to the black hole's gravity it emits intense energy, which can push the surrounding matter outward. This is how the galactic wind is created.
Then the question is when did galactic winds come into existence in the Universe? This is a key question because it is related to an important problem in astronomy: how did galaxies and SMBHs coevolve?
In an attempt to find galactic winds in the ancient Universe, an international research team led by Dr. Takuma Izumi, a project assistant professor at the National Astronomical Observatory of Japan (NAOJ), used ALMA to observe HSC J124353.93+010038.5 (hereafter J1243+0100), an extremely distant galaxy with a SMBH, which was discovered by the Subaru Telescope. Detailed analysis of the ALMA data revealed that there is a powerful, high-speed gas flow moving at 500 km per second in J1243+0100. The gas flow is truly a galactic wind, and it is the oldest observed example of a galaxy with a huge wind of galactic size.
The team also measured the motion of the quiet gas in J1243+0100, and estimated the mass of the galaxy's bulge, based on its gravitational balance, to be about 30 billion times that of the Sun. The mass of the galaxy's SMBH, estimated by another method, was about 1% of that. The mass ratio of the bulge to the SMBH in this galaxy is almost identical to the mass ratio of black holes to galaxies in the present-day Universe. This implies that the coevolution of SMBHs and galaxies has been occurring since less than a billion years after the birth of the Universe.
"Ultra-wide field and highly sensitive observations using the Subaru Telescope and HSC have revealed more than 100 SMBHs in the very distant Universe," comments Dr. Izumi. "We are planning to observe a large number of such objects with ALMA in the future, and hope to clarify whether or not the primordial coevolution seen in this object is an accurate picture of the general Universe at that time."
Note 1: For more information, please see the Subaru Telescope press release issued on March 13, 2019, "Astronomers Discover 83 Supermassive Black Holes in the Early Universe." The number of galaxies with SMBHs discovered was 83 at the time of this announcement, but the number of discoveries has now increased to over 100.
This research will be published in the Astrophysical Journal on June 14, 2021 (Takuma Izumi et al. "Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). XIII. Large-scale Feedback and Star Formation in a Low-Luminosity Quasar at z = 7.07".)