National Astronomical Observatory of Japan

 Ken-ichi Tadaki

I have always pursued what I wanted to do. That is my strength.

ALMA Project
Project Assistant Professor

Ken-ichi Tadaki

Seeing our work published in “Nature” gave me a great sense of achievement.

My job is to observe and study distant galaxies as far as 10 billion light-years away by using huge telescopes, like ALMA in Chile and the Subaru Telescope in Hawaiʻi. Previously, we studied a monster galaxy located 12.4 billion light-years away with unprecedented resolution and successfully created a map that shows the distribution of molecular gases. This research was announced in 2018, both inside and outside Japan, and appeared in the scientific journal Nature(note 1). “Our work has been published in Nature!” Such a feeling gave me a great sense of achievement.

In 2020, we launched a unique project called “Subaru Galaxy Zoo Project.” (note 2) The idea for this project popped up in my mind when I was reading a book I found in a library. It was about AI and said that AI has become able to identify animals, which led me to realize that this technology might be applicable to galaxy classification. In the past, there was a project called “Galaxy Zoo,” in which the sheer number of volunteers online classified galaxies by hand. But I thought, “What if we use data from the more powerful Subaru Telescope and have AI do the same task?” and we did it actually.

(note 1) Unstoppable Monster in the Early Universe - ALMA obtains most detailed view of distant starburst galaxy (ALMA Project)

(note 2) Subaru Galaxy Zoo Project with Artificial Intelligence (Subaru Telescope)

Ken-ichi Tadaki during the interview.

It is important to pursue what you really want to do.

During the two years of my master’s program, I was at JAXA and conducted my research project using the 45-m Radio Telescope of Nobeyama Radio Observatory. However, I wanted to see even more distant parts of the Universe, and this was where the Subaru Telescope had an edge over other facilities. So, I came to NAOJ to do my Ph.D. At that point, I felt even more that I was doing astronomy, and it was pleasing. Some time later, I was referred to a mentor at the Max Planck Institute for Extraterrestrial Physics in Germany, where I studied for two and a half years. My mentor there was Prof. Reinhard Genzel. He won the Nobel Prize for Physics in 2020, which surprised me a lot. His comments were incisive, but being invited to a party at his home was a particularly good memory among many others. Around this time, I started to use ALMA as well. The Nobeyema 45-m Radio Telescope and ALMA observe radio waves, and the Subaru Telescope measures visible light. It is a great advantage to be able to see both visible light and radio waves.

Starting my academic career as a university student, I have changed my research focus during the course and have spent a few extra years. But given that our academic careers last for decades, a few years of delay is not a big deal. In fact, I think it is more important to experience bits of different fields and to faithfully pursue what you really want to do.

I want to trace back the cosmic history through distant galaxies.

The Subaru Galaxy Zoo Project is still in its test phase. In the future, I would like to do more complex classification and measure the shapes of galaxies back to 2-3 billion years ago to trace back the cosmic history.

Narrowing down the number of observation targets, I also hope to use ALMA to observe more distant galaxies to investigate precisely what ancient galaxies were like. It is one of my primary research interests to capture high resolution pictures (or images) of galaxies, thereby creating a map of galaxies.

I would also like to use the Thirty Meter Telescope (TMT), a joint effort among Japan, the U.S.A., Canada, and other countries that is currently underway. The Subaru Telescope can see a wider swath of the sky, while TMT will reveal a more detailed view of the heavens. It would be nice if I could fully exploit both telescopes and further advance my research.

Ken-ichi Tadaki in the ALMA Building.
Ken-ichi Tadaki posing with a scale model of the Subaru Telescope.

Spending free time with family

During my two and a half years in Germany, I had my first son. However, after returning to Japan, we were unable to enroll our son in preschool because applications for the next school year had already ended. So, it was a great help that NAOJ’s childcare room still had a vacancy and accepted our son. Municipal childcare facilities may refuse to accept children if their mothers do not work, but the childcare room here will enable them to drop off their children and then go job hunting.

It takes me about a 10-minute bike ride from my workplace to home, and I have dinner at around six every evening with my family gathered around the table. If I worked in the city center, it would be difficult to live near the workplace. This is also a good point of working in NAOJ.

Another interesting aspect of NAOJ is that it offers a range of club activities frequently conducted on campus. I have played badminton since I was in junior high school and still love it. There is a badminton competition between university employees, in which NAOJ has even won the title. I think that, in terms of a working environment, NAOJ may be an ideal place.

Ken-ichi Tadaki posing with a scale model of ALMA.

Interview Date: December 17, 2020 / Published June 28, 2021
Interview & Article: Masami Usuda / Translation: Ryo Sato and Ramsey Lundock / Photo: Yutaka Iijima
With a few exceptions, the contents of this article are as of the interview date.