Disclaimer: machine translated by DeepL which may contain errors.
~ Message from a graduate student~.
Mystery of Cosmic Reionization Probed by Subaru Telescope
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| Rikako Ishimoto |
| Department of Physics First-year doctoral student |
| Birthplace Tokyo, Japan |
| High School Private Jogakuin High School |
| Faculty The University of Tokyo Faculty of Science |
What is the history of the universe and how has it shaped the present universe and us? This is one of the major questions in astronomy, but since the evolution of the universe takes a very long time, we cannot, for example, observe the process of the birth and evolution of a single galaxy. Instead, one way to explore the history of the universe is to observe the distant universe. Since the speed of light is finite, light arriving from the distant universe must have departed from the past universe and reached the earth over a long period of time. Therefore, by observing distant celestial objects, we can investigate the state of the past universe while still living in the present day.
My research is focused on the cosmic reionization period, which is about 13 billion years ago. Since the age of the universe is said to be about 13.8 billion years, we can say that it was not so long after the birth of the universe, considering the history of the universe. Immediately after the Big Bang, the universe was hot, and the gas in space was in a plasma state with electrons separated from the nucleus. The light from the stars and galaxies that were born after that caused the electrons to leave the nucleus again, creating the ionized universe as we know it today. This is cosmic reionization, a major event in the early universe that depends on the type, density, and distribution of astronomical objects in the universe at that time.
Observational studies have shown that the progress of reionization varies from place to place even at the same epoch. What is causing these differences, even though the universe is generally uniform? One of the most likely causes is fluctuations in the intensity of UV radiation from the surroundings (UV radiation field) and fluctuations in the temperature of the intergalactic gas, and it was predicted that one could distinguish which of these two causes was responsible by examining the density of galaxies in locations where reionization progresses extremely quickly or slowly (red and blue lines in the figure). (red and blue lines in the figure).
We used the Subaru Telescope to observe the extremely fast and slow reionization progression. The Subaru Telescope is a large telescope located at the summit of Mauna Kea in Hawaii, and for this study we used the Hyper Suprime-Cam camera, which has the largest field of view in the world. The distribution of galaxies at that epoch in the obtained images showed that there were fewer galaxies in areas where the reionization process was slow, whereas there were more galaxies in areas where the reionization process was fast. In addition to the results of the previous study, the density distribution of galaxies in the early stages of reionization was also examined, and it can be said that the cause of the non-uniformity of reionization is the fluctuation of the ultraviolet radiation field (Figure).
Observations of the universe through telescopes provide a glimpse into the state of the universe hundreds of millions of years ago. I think it is one of the most exciting aspects of astronomy to be able to explore events that occurred long before the birth of mankind. Observations of the distant universe are progressing rapidly, and we will gradually learn more about how the present universe in which we live was formed.
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The Rigaku-bu News, March 2023