Universe of Spectroscopy

Author: Nobunari Kashikawa

What would you like to introduce to readers in this series?

In this “Universe of Spectroscopy” series, I introduced “multi-object spectroscopy”. Multi-object spectroscopy is determining the universal and general properties of celestial objects through simultaneous spectroscopy of many objects.

For example, it is difficult to identify the general characteristics of the Japanese by only seeing one Japanese. You can start to see it by investigating many Japanese people young and old, male and female, from Hokkaido to Okinawa. Determining the general properties through the statistical analysis of a large sample is required for astronomy.

Especially, this approach has become important for the properties of distant galaxies which are hard to find. For the case of the galaxies at redshift 6.5 introduced previously, based on not just their general properties, but also on the statistical differences compared to slightly closer galaxies, we found that the change of ionization state of cosmic space. (This is called the re-ionization of the Universe.) It can be said that these results are possible only through multi-object spectroscopy.

My research field and current interests:

After this research, we continued the search for distant galaxies with the Subaru Telescope. The farthest was at redshift 7.215 (12.91 billion light-years from Earth.) Also, we conducted similarly energetic multi-object spectroscopy for an area slightly closer, but still at redshift 6 (12.71 billion light-years) and found an area where many galaxies were clustered together = an early galaxy cluster. Moreover, we want to expand our research to include quasars and define the state of the early Universe through a systematic survey using Hyper Suprime-Cam.

In addition, I still do not have any ideas for an easier to understand Japanese word for “redshift” which is written in the image caption of this column, even though I assigned the problem to students. This is a more difficult problem than the mysteries of the Universe.


Nobunari Kashikawa
TMT Project Office
Job Title
Associate Professor
Field of Expertise
Galactic Astronomy