Abstract

The cosmic infrared background light is known to have energy comparable to the optical one, suggesting the importance of infrared observations to understand the other aspect of the universe obscured by cold materials. In this seminar, I will present our latest research on the formation and evolution of galaxies at z~5-7 in a wide range of scales, including active galactic nuclei (<100 pc), interstellar (ISM; ~100 pc to 5 kpc), and circumgalactic media (CGM; ~5-20 kpc), based on the latest (sub)millimeter observations with ALMA and NOEMA. I will discuss what is taking place in the cold side of the early universe, highlighting three recent discoveries: i) the CGM-scale [CII]158um gas halo, ii) the difference between the 3D structure of neutral and ionized gases in the ISM, and iii) the young quasar forming in a dust-enshrouded starburst.