談話会
Colloquium

Yutaka Ohira (U. Tokyo)
First cosmic-ray acceleration and magnetic-field generation in the early universe
The magnetic field and cosmic rays (CRs) are ubiquitous in the current Universe and play various roles in different environments. The energy densities of the magnetic field and CRs are about 0.1-1 eV/cm^3 in our Galaxy, which is comparable to that of thermal particles. Therefore, the magnetic field and CRs are thought to have important roles in galaxies. Nevertheless, it has not been well understood when, where, and how the magnetic field and CRs are first generated since the Big Bang. In the standard picture, CRs are thought to be accelerated after the magnetic field with a sufficiently large scale is generated and amplified. Recently, we proposed a new paradigm that the magnetic field with a small scale is generated by the Weibel instability in the first supernova remnants at z~20; the small scale magnetic field and the supernova remnant shock accelerate the first CRs by the diffusive shock acceleration; the first CRs generate the magnetic field with a large scale while propagating to the intergalactic space. In this talk, we are going to talk about the first CR acceleration mechanism and new generation mechanisms of the large-scale magnetic field by the first CRs.

Seiji Fujimoto (Niels Bohr Institute)
Exploring the Cold Universe: From Obscured Active Galactic Nuclei, Inter-Stellar to Circum-Galactic Media at z~5-7
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 medium (ISM; ~100 pc to 5 kpc), and circumgalactic medium (CGM; ~5-10 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.

Yudai Suwa (U. Tokyo)
Modeling supernova neutrino emissions toward physics and multi-messenger astronomy in the next Galactic supernova
Neutrinos are guaranteed observable from the next Galactic supernova (SN). Optical lights and gravitational waves are also observable but can be difficult to observe if SN location in the galaxy and the explosion details are unsuitable. The key to the next SN observation will be understanding various physical quantities using neutrinos first and then connecting them to other signals. In this seminar, I will discuss what physical quantities (e.g., mass and radius of neutron stars) can be extracted from observations using large statistical neutrinos as physics probes, and how to use these extracted physical quantities to link with the explosion mechanism of SN and multi-messenger observations.