Dream big and aim beyond galaxies｜リガクル[RIGAKU-RU]

Nuo Chen, a graduate student at the School of Science, grew up in China while enchanted by Japan’s culture. What will his research on distant galaxies reveal about our universe?

From Shanghai to Tokyo

My parents worked for a Japanese company in Shanghai, so I liked Japanese culture and anime, which motivated me to study in Japan. I have been watching Japanese anime since childhood. The first anime I watched was Gundam Seed. I also learned Japanese for a year before taking the entrance exam for the University of Tokyo.

I have been in Tokyo for four years doing my master's course and now my Ph.D. In my experience, Tokyo is much quieter and cleaner, though the living expenses are like those in Shanghai. Because the Japanese people are more well-mannered (once I lost my wallet and someone picked it up and gave it to the police), I like living here while being closer to my family living in China.

A budding interest in space

As a child, I wanted to become a spaceman (astronaut). I enjoyed watching stars and the moon and wondering how they are unreachable to most people. In 2007, I had a chance to contact the astronauts at the International Space Station over the amateur radio through the ARISS School Contact Project. I asked them about life aboard the space station. Two years later, due to bad weather in Shanghai, I could not see the solar eclipse even though I was looking forward to it. To make up for it, my father and I went to Yellowstone National Park in 2017 to see a solar eclipse. I photographed various stages of the eclipse and sent the photos to a magazine in China. It felt amazing. These experiences fueled my interest in space and astronomy. During my undergraduate years, I led the Astronomy Club at the university and continued astrophotography as a hobby.

A composite image of a solar eclipse. © Nuo Chen.

Because I cannot carry my amateur astronomy telescope while traveling, I take my digital camera and a small tripod to photograph the night sky. Recently, when I visited Australia on a project, I got to take photographs at the Siding Spring Observatory near Sydney. It was late at night when we heard noises in the bush. I went closer to inspect. It was kangaroos (laughs).

Kangaroos near the Siding Spring Observatory telescope. © Nuo Chen.

Research abroad

I could visit Macquarie University in Sydney, Australia, thanks to the Graduate Research Abroad in Science Program (GRASP^＊1) funded by the School of Science. I focused on drafting my first research paper and conducting data analyses there. Experiencing the research atmosphere in Australia was interesting to me. For example, on Friday afternoons, they go to the bar on campus and talk about science and life. In Japan, I seldom talk with people because Japanese people are a bit shy. But in Australia, I talked to many people from different scientific fields and cultures.

Blossoming into curiosity beyond our galaxy

During, my Master course, I studied distant galaxies (several billion light years away) in the infrared using telescopes, such as the Subaru Telescope and the Magellan Telescope. Because these galaxies are so distant, the optical light they emitted is red-shifted to infrared The data we obtained is called photometric data, which contains spectral information (like a fingerprint) about the galaxies . To extract properties of the galaxy, like mass and age, I wrote code to fit the known spectra of the stellar population to the photometric data. We call that Spectral Energy Distribution fitting. Using this method, we got valuable information about the galaxies which we cannot gain with only photographs.

An interesting spectral feature we found is that these distant galaxies emit a strong emission line from ionized hydrogen called H-alpha emission, a good indicator of the birth rate of stars in a galaxy. The galaxies with strong H-alpha emission are newly formed galaxies. We also found another remarkable emission line from ionized oxygen, called [O III] (read O-3) in these galaxies. In the local universe, galaxies with strong [O III] are called Green Pea galaxies (named so because of their greenish appearance). The Green Pea galaxies are young galaxies with remarkably high star formation rate in the local universe. The aim in my Master course was to understand their detailed properties of such green pea galaxies at high redshift.

I am now working on the data obtained from the James Webb Space Telescope (JWST) launched into space at the end of 2021. As the telescope is in space, unlike ground-based telescopes, the Earth’s atmosphere does not distort or affect the data. The efficiency of the 1-hour exposure time on JWST far exceeds the 12-hour exposure from a ground-based telescope, giving us the deepest data better than any ground-based telescope. Also, JWST provides high-resolution data, around 5 times better than the best ground-based telescope. These two factors mean we can find even the faintest galaxies in the distant universe and learn more about their physical properties, such as their shape. It is a new world through this marvelous telescope.

From the data, we can also understand how galaxies were formed and evolved to what we see today. Since the galaxies and inter-galactic mediums are evolving at different rates, present galaxies and those at 1 billion years after the Big Bang differ in properties, such as their star formation rates and metallicity. Such cosmological evolution is quite interesting to study.

The importance of a scientific aim

While at the University of Tokyo, I have learned that having a defined scientific aim is more important than anything. Programming skill is not a problem; if you have any coding problems, you can ask ChatGPT to fix them. It can do it for you, and you can always fix the code if it is inaccurate. As a researcher, the priority is to find unknowns in our research field.

Future through the academic telescope

After graduating, I plan to work as a postdoc in Japan, and then another postdoc in Europe, Australia, or the United States. Eventually, I want to get a research position at a university or an observatory.

GRASP^＊1　https://www.s.u-tokyo.ac.jp/ja/offices/ilo/grasp/application.html

Redshift^＊2　https://www.esa.int/Science_Exploration/Space_Science/What_is_red_shift

※Year of Interview:2023
Interview and text: Ravindra Palavalli Nettimi
Photography: Junichi Kaizuka
The interviewee approved the edited and concise version of the interview.　

Nuo Chen

2nd-year doctoral student, Department of Astronomy

Nuo was born in Shanghai, China. After completing his bachelor's degree at Shanghai Jiao Tong University, China, he enrolled in the University of Tokyo for his master’s degree in 2020. He started his doctoral degree at the School of Science in 2022. In his leisure time, Nuo plays soccer, cycles, or watches anime.