Researchers have finished equipping the Subaru Telescope with a new special “compound eye,” culminating several years of effort. This new eye is an instrument featuring approximately 2,400 prisms scattered across the extremely wide field of view available at the Subaru Telescope’s primary focus, allowing for simultaneous spectroscopic observation of thousands of celestial objects. This unrivaled capability will help researchers precisely understand the formation and evolution of galaxies and the Universe. Among 8-meter-class telescopes, the Subaru Telescope is the most competitive with the largest survey capability in the world. This instrument, the Prime Focus Spectrograph (PFS), will be ready to begin scientific operations in February 2025.

PFS will be one of the flagship instruments of the “Subaru Telescope 2.0 ” era. Taking advantage of the Subaru Telescope’s ultrawide field of view, approximately 1.3 degrees in diameter at the prime focus, and world-renowned large light-gathering power, PFS will position 2,400 fibers to collect light from celestial objects and simultaneously obtain spectra across the entire visible light range and part of the near-infrared band. Just like the compound eyes of insects, each facet (fiber) focuses on a different direction to cover a wide area while perceiving the colors of light from that direction. This highly ambitious instrument will dramatically enhance the Subaru Telescope’s spectroscopic observation efficiency.

Spanning nearly 15 years with support from industrial partners around the world, the development of PFS has been led by an international collaboration of over 20 research institutions in Japan, the U.S., France, Brazil, Taiwan, Germany, and China. Notably, the University of Tokyo Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI) has taken the lead in proposing and developing the instrument as well as planning large-sky survey observations, with the goal of testing various theoretical models about the formation of the Universe. The National Astronomical Observatory of Japan (NAOJ) has also played a central role, participating in the development of the instrument and overseeing the coordination of the project, while also being responsible for the acceptance and operation of the instrument.

The PFS team plans to carry out a large-sky survey program over the next five or so years, utilizing a total of 360 nights of telescope time. This survey will take spectra of millions of distant galaxies, as well as hundreds of thousands of stars in the Milky Way and our neighboring Andromeda Galaxy.