Subaru Telescope 2.0

How galaxy formation and evolution are related to the star formation in the Universe should be elucidated to determine the materials' evolution. Subaru Telescope 2.0 investigates how dark matter, galaxies, and intergalactic gases impact each other by optical and infrared observations of the wide sky coverage and looks into galaxy formation and evolution in the Expanding Universe in depth by analyzing it at the following four stages:

(1) Birth of Galaxies: Probe first celestial objects
The present Universe is populated with distinct types of objects and structures in terms of characteristics and scales. First stars and galaxies, which formed at the beginning of the Universe, played an important role in the history of the formation of many kinds of objects. They are the first sources of heavy elements and also the seeds of massive black holes. Yet, how they formed and evolved has not been revealed.

The Subaru Telescope has discovered more than 1,000 infant galaxies that existed within 1 billion years of the Big Bang and indicated that during this period, stars actively formed (the Subaru Telescope’s observation result, September 26, 2019, and others). HSC has played a significant role in these discoveries. Subaru continues HSC’s search and conducts large-scale spectroscopic observations by PFS for HSC’s findings to study the formation of large-scale structure in the early Universe, and evaluate the nature of galaxies with a very high level of statistical precision. The Subaru Telescope offers the unrivaled capability to achieve this research.

Yet, with little progress in the search for galaxies that existed within 5 billion years after the Universe began, only 10 candidates have been found. This phase underwent an active transition from a neutral to a reionized Universe, called the reionization of the Universe. Finding out which objects caused the reionization and how it proceeded is the key to understanding the evolution of the early Universe.

Given that the light from galaxies emitted during this period is redshifted to near-infrared wavelengths, ULTIMATE-Subaru is employed for wide-field near-infrared survey. To analyze their nature, we aim to discover dozens of candidates of the first galaxies assumed to have existed during this time. At the same time, the luminosity function, the number density of galaxies per brightness, which means how many galaxies of what brightness exists, which is currently not yet available because there are too few discovered objects, is determined. The luminosity function of the earliest Universe will provide essential information for revealing how galaxies formed. Further, we look into the earliest phase of formation of the large-scale structure of the Universe by finding possible first galaxy groups, which are the seeds of larger structures. If Subaru Telescope 2.0 discovers the first galaxy candidates, they will become the target of detailed observation by the next generation of extremely large telescopes, such as the Thirty Meter Telescope (TMT) and ALMA. We team with those telescopes for coordinated observation to provide detailed views of individual candidates.

(2) Growth of Galaxies: Origin of galaxy shapes
Studying how galaxies formed and evolved is one of the important historical events of the Universe after the first celestial bodies formed. Based on past observations, it is known that two billion to four billion years after the Big Bang was the most active period of star formation and rapid growth of galaxies. Many galaxies are thought to have developed different shapes (spiral, elliptical, etc.) that we can currently see, but little is known in detail.

We conduct research on the evolution of galaxy shapes from multiple perspectives. Because the morphology of galaxies is considered to be closely related to their gases, we analyze gases within and outside galaxies of this period through spectroscopic observation by PFS. In addition, our PFS observation also extends to many galaxies that existed four billion to seven billion years after the Big Bang when more time elapsed. By tracking how galaxies grew in detail and detecting the large-scale structure of the Universe, we explore the relationship between the growth of galaxies and the large-scale structure. In this observation, galaxies detected by HSC's survey are analyzed by PFS. In parallel, capitalizing on ULTIMATE-Subaru's high-resolution imaging, we will directly capture the shape changes of galaxies that existed two billion to seven billion years since the Big Bang. Combining all the forces of the Subaru Telescope's imaging and spectroscopic capabilities will provide an answer to this question.

(3) Maturity of Galaxies: Maturity process
In the nearer Universe that has existed since 10 billion years after the Big Bang, ULTIMATE-Subaru provides high-resolution views that allow us to distinguish individual stars and gas clouds of each galaxy, setting the sight on the maturity process of galaxies. The nearby galaxies appear to be widely spread, but ULTIMATE-Subaru’s field of view has a significant advantage in observing an entire galaxy for this purpose.

(4) Our Galaxy
The Milky Way, where we stand, can be looked into in the closest way as one of the galaxies in the maturity stage. We conduct wide-field observation of the central region of the Galaxy and probe black holes by analyzing the gravitational micro-lensing effect to identify the number of black holes, mass, and spatial distribution in the Galaxy.

“From the cradle to the grave of the galaxy”: Science charted by Subaru Telescope 2.0 with ULTIMATE-Subaru. Subaru Telescope 2.0 leads the way in revealing the history of galaxy formation and evolution. Optical and infrared observations cover multiple phases or distances of the Universe.