This fiscal year, I focused on observational studies of the co-evolution of supermassive

black holes and their host galaxies in the early universe, primarily using my PI

observations of the James Webb Space Telescope (JWST), a 6.5-meter space infrared

telescope. In particular, in my first-author paper published in Nature Astronomy (Onoue et

al. 2025), I provided new insights into the connection between black hole growth and

galaxy evolution only 900 million years after the Big Bang, based on the detection and

stellar population analysis of host galaxies of low-luminosity quasars at redshift 6. This

result was obtained from 12 quasars that were originally discovered by Subaru Telescope.

For one object in particular, J2236+0032, I was able to capture a phase in which the host

galaxy had already matured, reaching a stellar mass of 10 billion solar masses, and its star

formation had been quenched by an accreting massive black hole residing its center. This

study is the first in the world to achieve such a detailed characterization of the properties

of distant galaxies hidden beneath the glare of luminous quasars, which were only

possible down to redshift 1-2.

As a key result of the JWST project, we report the distribution of the distant quasars and

their host galaxies, where we advocate that the stellar to BH mass relation does not

largely evolve from redshift 6 to 0, namely the current universe. We are now planning to

extend this study with a x4 larger sample in order to more accurately constrain the mean

mass ratio and its intrinsic scatter, which may contain information of the seed black hole

formation.

In addition, I led new observations with the Subaru Telescope's new instrument, Prime

Focus Spectrograph (PFS). The target was a proto-cluster field around a luminous quasar

at z=6.6. Taking advantage of the PFS's capability to perform multi-fiber spectroscopy

over R~200 coming mega parsec at z~6, I will use this data to confirm the richest galaxy

environment supplying cold gas to a monster black hole.

In recognition of these world-leading observational achievements as well as my past

research activity, I was awarded the Young Astronomer Award of the Astronomical

Society of Japan.