Galaxy clusters are important probes in the study of galaxy formation and cosmology. Dense spectroscopy is a unique tool for investigating cluster properties and their galaxies. In this talk, I will highlight the diverse applications of dense spectroscopy, including the derivation of velocity dispersion functions and the novel technique of spectroscopic weak lensing tomography. These approaches will be important tools for future large-scale spectroscopic surveys.
The next-generation survey observations for cosmological studies, such as Rubin and Euclid, are expected to start observation this year. To reveal the mystery of dark energy and dark matter in the Universe, these surveys will bring us unprecedented constraining power on cosmological parameters and ample opportunities to test beyond the standard cosmological model (LCDM). To understand where we are standing with the most recent observations, in my talk, I will overview the weak lensing analysis results of current surveys as well as the challenges, including the baryonic feedback effect. As a main builder of the Kilo-Degree Survey (KiDS), the current European Survey team, I will also introduce upcoming updates on the last release of the KiDS (KiDS Legacy) data, whose scientific results are scheduled to be announced this Autumn.
I'll present a novel method of probing dark-matter properties by using the mass spectrum of gravitational-wave sources.
Asteroids are considered to be among the most primitive celestial bodies in our solar system and are crucial for understanding the origin and formation processes of the solar system. Furthermore, the significance of asteroids has been increasingly recognized, both in terms of planetary defense and possible space resource utilization. Astronomical observations have been one of the most powerful methods to investigate the physical properties of asteroids, enabling us to obtain information such as orbit, size, shape, spin state, and surface properties. In this talk, I will introduce an overview of how astronomical observations have been used to study the physical properties of asteroids. Specifically, I will present the outcomes of large-scale survey observations and discuss the synergistic effects of utilizing the observation results from various surveys. Additionally, I will present the interplay between space missions and astronomical observations in asteroid research, highlighting their complementary roles and the unique benefits each approach provides.
The nearby radio galaxy M87 is a prime target to study black hole accretion and jet formation. Event Horizon Telescope observations of M87 in 2017, at a wavelength of 1.3 mm, revealed a ring-like structure which was interpreted as gravitationally lensed emission around a central black hole. Here we report new images of M87 obtained in 2018, at a wavelength of 3.5 mm, showing that the compact radio core is spatially resolved. High resolution imaging reveals a ring-like structure of 8.4-1.1+0.5 Schwarzschild radii in diameter, ~50% larger than that seen at 1.3 mm, with the outer edge at 3.5 mm also being larger than that at 1.3 mm. This larger and thicker ring indicates a significant contribution from the accretion flow with high self-absorption opacity effects, added to the gravitationally lensed ring-like emission. The new images show that the edge–brightened jet connects to the black hole’s accretion flow. Close to the black hole, the emission profile of the jet launching region is wider than the expected profile of a black hole driven jet, suggesting the possible presence of a wind associated with the accretion flow. A paper summarizing these findings has been published in the journal Nature. During this presentation, I will discuss the physical significance of the M87 black hole images captured at 1.3 and 3.5 mm, as well as the experiments underway in Korea that aim to provide further insight into the characteristics of this black hole.
Understanding galaxy evolution is one of the big subjects in modern astronomy. Galaxy clusters and superclusters, which sit on the top of the hierarchy of structure formation in the universe, are valuable objects to witness various types of galaxies and environments and study how the properties of galaxies change with their surroundings. Submm galaxies (SMGs) are holding hints to reveal the mystery of star formation history in the early universe. In this talk, I will introduce the study of galaxy evolution in the galaxy clusters with the large-scale structure environment in the SA22 field. From this study, we checked the `web feeding model,’ which is that more linked (with their environment) galaxy clusters have less quenched population by investigating the correlation between properties of confirmed galaxy clusters and the large-scale structure environment. Second, I will present the newly found submm galaxies(SMGs) with JCMT SCUBA-2, star-forming populations having the key to revealing the hidden star formation in the universe, in the JWST Time Domain Field near the north ecliptic pole. I also introduce the preliminary image of the JWST for these submm galaxies.
Currently, the Moon has dispersed crustal magnetic anomalies instead of a global magnetic field like the Earth. The magnetization of the lunar crust has been studied for many years using magnetometer data obtained on the lunar surface, orbiting spacecraft, and lunar samples returned during the Apollo missions. Recent missions with polar orbits, such as Lunar Prospector and Kaguya, have expanded these measurements globally. Despite knowing that the lunar crust is magnetized since the Apollo era, we still lack a complete understanding of how crustal magnetism was generated. Additionally, due to the absence of a global magnetic field and atmosphere, solar wind particles directly impact the lunar surface, leading to a different solar wind interaction with the Moon compared to Earth. The wave activities generated by solar wind interaction with the Moon have been studied for many years. However, we still do not completely understand how and where they are generated. In this talk, I will present the magnetic anomalies on the Moon and the source model of lunar magnetic anomaly. I will also present ultra-low frequency (ULF) waves generated by solar wind interaction with the Moon and the generation mechanism of the observed lunar waves.
AGB stars are very important in stellar evolution. The death of most stars with 1-8 solar mass is a result of heavy mass loss in this phase. After losing the stellar envelope, they evolve to post-AGB stars with higher temperature at almost constant luminosity. In observations, the gas envelope evolves to asymmetry structures and massive material is suddenly ejected by bipolar or multipolar outflows. These objects are classified as pre-planetary nebulae (or PPN) because it takes only a few hundred years evolving into the planetary nebula phase, leaving a white dwarf and ionized gas envelope in space. When we look into the sky, there are various shapes of the planetary nebulae. Studying the properties of outflows can help us to understand the complex physics and chemistry in the planetary nebulae. I’ll present recent research on three of our targets, CRL 618, Cotton Candy Nebula, and V Hydrae, possessing multi-directional and multi-epoch outflows. We explore a possible scenario where the mass loss of AGB stars could be periodically accreted by a companion passing of the periastron in a high-eccentricity orbit, forming disks and multipolar outflows.
Planets form in protoplanetary disks around young stars. As most young stars form in cluster environments, planet forming disks are exposed to various levels of external UV radiation. Such external UV radiation plays an important role in protoplanetary disk evolution affecting disk lifetime, disk properties, and planet formation. Photoevpaorating protoplanetary disks (proplyds) are found near O stars in the Orion Nebula Cluster (ONC), which harbors over hundreds of them. We have identified more proplyds around two other young star forming regions in Orion A and B clouds: NGC 1977 and NGC 2024. Proplyds are found mostly in Orion in vicinity of O stars (ONC), but as low as B1V star (NGC 1977) providing diverse ranges of UV environments. In this talk, I will present recent work on properties of Trapezium cluster at the heart of Orion Nebula, and discovery of proplyds in NGC 1977 and NGC 2024. These clusters provide excellent laboratory to study interplay between UV radiation from massive stars and protplanetary disks in strong (ONC, NGC 2024) and intermediate (NGC 1977) UV radiation environments. NGC 2024 is unique as it provides the youngest age among the three regions (age <0.5-1 Myr), while NGC 1977 provides the weakest UV environment where proplyds are discovered. I will also present our kinematic studies of the proplyds and non-proplyd young stars in ONC and NGC 1977, and explore possible explanations for "proplyd life time problem".
Previous simulation studies suggest that dust-obscured AGNs appear for a certain period when merger-driven star-forming galaxies evolve to unobscured AGNs. The dust-obscured AGNs would have red colors due to the dust extinction from their host galaxies, and they are expected to have enhanced black hole activities than unobscured AGNs. Red AGNs have very red colors, and they have been suspected as the intermediate-stage, dusty AGNs. However, it is not yet clear if red AGNs really correspond to the dusty young AGNs due to a lack of intrinsic properties of red AGNs. For unveiling the intrinsic properties of red AGNs, we study unobscured and red AGNs. There are three main themes: (i) derivation of new black hole mass estimators that can be used for red AGN study; (ii) investigation of red AGN selection methods to test its usefulness to identify dusty red AGNs; and (iii) investigation of the accretion rates of red AGNs to see if they have the properties as predicted in the simulation studies.
본 발표는 “우주법의 구조와 미래”(The Structure and Future of Space Law)에 관한 것으로 1957년 10월 4일 소련의 스푸트니크(Sputnik) 1호 발사로 우주활동이 본격적으로 전개되어 가자 이를 규제하기 위한 우주법이 탄생하면서 1967년 우주조약(Outer Space Treaty)을 비롯한 1968년 구조협정(Rescue Agreement), 1972년 책임협약(Liability Convention), 1975년 등록협약(Registration Convention), 1979년 달협정(Moon Agreement) 등 우주관련조약들과 관습법(customary law) 및 연성법(soft law)의 의미를 살펴볼 것이다. 최근 미국이 1970년대 아폴로 프로젝트 이후 50 여년 만에 달에 우주인을 보내기 위한 유인 달탐사 프로그램인 ‘아르테미스 프로그램’을 진행하면서 수립한 현재 미국을 비롯한 23개국이 동참하고 있는 ‘아르테미스 약정’(Artemis Accords)은 기존 우주법과 어떠한 관련을 가지고 있는가 하는 문제도 살펴볼 것이다. 마지막으로 우주법의 미래는 어떻게 전개될 것인가 하는 문제를 살펴볼 것이다.
The talk discusses about the current development activities of a small satellite launch vehicle mostly by the domestic startup, Perigee Aerospace Inc.
달, 화성, 소행성 등에 대한 우주탐사는 이제 하나의 산업이자 경제가 되고 있다. 다른 영역에서의 경제학과 마찬가지로 우주탐사 경제학에서도 핵심은 바로 비용과 수익이다. 이 콜로퀴엄에서는 우주탐사에 드는 각종 비용들과, 수익 창출이 가능한 달, 화성, 소행성 자원들에 대해 알아본다. 구체적으로는 로켓 재사용으로 인한 발사비용 절감의 비밀, 달에서 채굴한 얼음을 지구 궤도에서 로켓 연료로 파는 사업 모델, 월면에서 채굴하는 He-3의 진짜 가치, 우주 엘리베이터의 실현 가능성, 다누리호가 선택한 WSB/BLT 궤도의 작동 원리 등에 대해 논의한다.