Cosmic ray flux is an important factor to response to solar activity. Its profile shows the decreasing shape by interaction of enhanced interplanetary magnetic field structure. When the solar eruptions such as solar proton events by flares arrive at the Earth, the profile of cosmic ray flux changes to sharp increasing shape at the ground neutron monitor. The former is well known as “Forbush decrease”, while the latter is known as “Ground level enhancement”. Cosmic ray working group began neutron monitor research in the early 2000s. At first, our group focused on the interaction between solar wind/interplanetary magnetic field and cosmic ray particles. The main topics are simultaneity of Forbush decreases, anisotropy of diurnal variation, relationship between solar proton events and ground level enhancements and so on. The first of neutron monitor by our group has installed at Daejeon in October, 2011. Another neutron monitor has been installed at Jang Bogo in Antarctica in December, 2015. The observational data by both neutron monitors have registered at Neutron Monitor Database (NMDB, http://www01.nmdb.eu/data/) on April, 2018. I introduce the brief installation of neutron monitor at Jang Bogo and the scientific achievements in cosmic ray research.
Alfvén waves are considered to be physically important in understanding physical processes in the solar corona such as nonthermal heating, solar wind acceleration and the abundance enhancement of low first-ionization-potential elements. However, it is still not clear how these waves are excited in the lower atmosphere. To reveal their physical origin, we have attempted to detect Alfvénic waves in the solar chromosphere using the spectroscopic method. By analyzing the spectral data taken by the Fast Imaging Solar Spectrograph of the 1.6 meter Goode Solar Telescope, we successfully detected the Alfvénic waves in the superpenumbral fibrils around a sunspot. This is the first spectroscopic detection of Alfvénic waves in the solar chromosphere. These waves are found to be physically associated with the three-minute umbral oscillation. We conclude that the Alfvénic waves excited by the slow-to-Alfvén mode conversion may prevail in the solar chromosphere.
An antenna and a receiver are needed to effectively receive microwave signals from the universe.
For such a receiver design, the experimental purpose and antenna characteristics should be considered.
In recent radio astronomy research, there is a demand for wideband multi-channel simultaneous observation of the receiver, and the design of a Compact Tripple Band Receiver is in progress.
In addition, this talk will introduce the design of a receiver for observation of CMB(Cosmic Microwave Background).
The receiver for CMB observation is very different from the conventional radio telescope receiver, and the design considerations are also different.
Finally, these receivers require cryogenic cooling during operation.
Various technologies and design methods for cryogenic cooling of receivers will be introduced.
Cosmology is a study to understand the origin, fundamental property, and evolution of the universe. Nowadays, many observational data of galaxies have become available, and one needs large-volume numerical simulations with good quality of the spatial distribution for a fair comparison with observation data. On the other hand, since galaxies' evolution is affected by both gravitational and baryonic effects, it is nontrivial to populate galaxies only by N-body simulations. However, full hydrodynamic simulations with large volume are computationally costly. Several attempts have been proposed to overcome such difficulties, such as applying alternative galaxy assignment methods or painting baryonic feature learned from hydrodynamic simulations to N-body simulations.
In this talk, I would like to introduce the MBP-galaxy abundance matching and mock galaxy catalogs of the Horizon Run 4 and Multiverse simulations, large-volume cosmological N-body simulations done by the Korean community. Also, I would like to briefly discuss how recent deep-learning techniques could help cosmological studies.
The advent of far-infrared/submillimeter observational facilities showed that a significant fraction of star formation is placed in heavily dust-attenuated galaxies in the early Universe. Due to the nature of galaxy spectral energy distribution and the effect of K-correction, galaxies selected at submillimeter wavelengths are likely to be vigorous star-forming high-redshift galaxies. Based on their characteristics – gas-rich, large stellar mass, frequent contribution from the active galactic nuclei – they are spotlighted to show the early stage of massive galaxy evolution. In this talk, I will introduce several ongoing submillimeter extragalactic surveys, particularly focusing on the JCMT/SCUBA-2 survey on the North Ecliptic Pole region.
The lives of galaxies and their supermassive black holes (SMBH) are probably intimately linked. Although mergers are considered a promising triggering mechanism for AGN activity, numerous studies have shown that AGN hosts are no more likely to appear morphologically disturbed than inactive galaxies. To study the AGN-Merger connection, i.e., merger activity in AGNs and AGN activity in merging systems, we run a suite of high resolution zoom-in cosmological hydrodynamic simulations. These simulations are post-processed with a radiative transfer code to generate HST mock observations of redshift 0.5