![[PukiWiki]](image/pukiwiki.png "[PukiWiki]")
Language: English
Abstract: The cosmic star-forming activity peaked at redshifts z=1-4 in the so-called "Cosmic Noon". This vigorous star production is driven by massive galaxies with star-formation rates (SFRs) 100-1000x higher than the Milky Way. However, it has long been unclear what causes these immense SFRs: are high-redshift galaxies forming stars very efficiently, or are they simply more gas-rich than present-day galaxies? Over the last decade, extensive surveys of molecular gas in high-z galaxies (via CO, dust, and [CII] emission) have established that they are indeed very gas-rich. However, a significant fraction of the molecular gas resides in diffuse, extended reservoirs, contributing little to the observed SFR. Maybe high-z galaxies have significantly enhanced star-forming efficiency after all? To answer this question, we need to study the dense gas from which stars form. As the low-J CO and [CII] emission trace gas down to densities of ~10^2 cm-3, we need to rely on emission lines of HCN, HCO+, and HNC. Unfortunately, as these lines are 10-100x fainter than CO or [CII], they have been detected in only a handful of high-z galaxies. I will showcase PRUSSIC: a comprehensive census of dense gas at high redshift with JVLA, ALMA - and a starring role by NOEMA. We find that high-z galaxies contain surprisingly little dense gas and have an enhanced star-forming efficiency. Moreover, we have obtained the first measurements of the HCN/HCO+/HNC ladders in high-z galaxies, allowing us to constrain the physical conditions (temperature, mechanical heating) of their dense-gas phase.
Language: English
Abstract: Jets launched by supermassive black holes transport relativistic leptons, entrained atomic nuclei, magnetic fields, and heat from the centres of galaxies to their outskirts and beyond. These outflows embody the most energetic pathway by which galaxies respond to the surrounding Cosmic Web. Understanding black hole feedback is an active research area, with implications for galaxy evolution, the stability of galaxy clusters, and the origin of cosmic rays, heavy elements, and magnetism in the intergalactic medium. The significance of this feedback to cosmology is ultimately bounded by the reach of black hole jets, and could be sweeping if jets travel far at early epochs. In this talk, I discuss the joint LOFAR–uGMRT–Keck discovery of a black hole jet pair extending over 7 megaparsecs, currently the largest known structure made by an astrophysical body. The outflow, seen 7.5 Gyr into the past, spans two-thirds of a typical coeval cosmic void radius, thus entering voids at high (∼96%) probability. This system demonstrates that black hole–launched jets can avoid destruction by magnetohydrodynamical instabilities over cosmic distances, even at epochs when the Universe was an order of magnitude denser than it is today. Whereas previously known extreme outflows appear predominantly launched by radiatively inefficient AGN, the current outflow is launched by a radiatively efficient AGN, the type most common at early epochs. If, as implied, a larger population of early void-entering outflows existed, then black hole jets could have played an important role in cosmic magnetogenesis. This outflow shows that energy transport from supermassive black holes operates on scales of the Cosmic Web and raises the possibility that cosmic rays, heavy elements, and magnetism in the intergalactic medium have a non-local, cross-void origin.
Language: 日本語
Abstract: 本講演は世話人の意向により日本語で行う。近年、極めて高い精度で、宇宙を構成するエネルギー成分の割合が報告されている。それらは、ダークマターが約27%、ダークエネルギーが約68%であり、目に見える通常の物質はたった約5%しかないことが明らかになってきた。我々のコミュニティーの次の目標は、ダークマターとダークエネルギーの正体を暴くことである。これは、必ず宇宙での観測を通して行わなければならない。なぜなら、独立した地上実験、例えば加速器実験などで新粒子が見つかったとしても、それが本当にこの宇宙に存在しているかどうかを証明しなければ、それらがダークマターやダークエネルギーであると同定されることは無いからである。今回、複数のダークマターとダークエネルギーの候補の理論モデルを解説し、将来の天文観測でのそれらの同定方法のアイディアについて紹介する。
Language: English
Abstract: It has been 40 years since the magnetized radio filaments were first reported toward the Galactic center (GC), the first hint of an energetic activity in this region. Since then, a large number of synchrotron emitting filaments has been discovered. In particular, the recent MeerKAT survey, which has been a gold mine in the study of the extreme environment of the GC, has increased the number of filaments by an order of magnitude. In this talk, I will discuss the statistical properties of the GC filaments, the comparison of the intracluster medium (ICM) and GC filaments, models of these enigmatic objects and the association of a milli-second pulsar powering a nonthermal radio filament near the Snake. Lastly, I will present nonthermal continuum emission from the Sgr B cloud and model the interaction of the cosmic-ray electrons incident on the Sgr B cloud.
Language: English
Abstract: The James Webb Space Telescope (JWST) is NASA’s flagship astronomy and astrophysics mission that was launched on December 25, 2021 and is operating in a halo orbit at Lagrange Point 2 (L2), 1.5 million km from Earth. With a 6.5-meter diameter primary mirror that is cooled to 50K and four infrared instruments, JWST is investigating four major science areas: ・First light and reionization: JWST is a powerful time machine with infrared vision that is looking back 13.5 billion years to see the first stars and galaxies forming in the early Universe. ・Assembly of galaxies: JWST’s unprecedented infrared sensitivity enables astronomers to compare the faintest, earliest galaxies to today’s spiral and elliptical galaxies, helping us understand how galaxies assemble over billions of years. ・Birth of stars and protoplanetary systems: JWST can see into massive clouds of dust that are opaque to visible-light observatories (like Hubble), where stars and planetary systems are being born. ・Planets and origins of life: JWST is telling us more about the atmospheres of extrasolar planets, and perhaps will even find the building blocks of life elsewhere in the Universe. In addition to other planetary systems, JWST will also study objects within our own solar system.
This presentation starts with the scientific motivation of JWST and reviews the major technological innovations that were needed to build the observatory. The four JWST instruments are presented with the optical path of the NIRSpec animated. The infrared focal plane arrays (FPAs) are presented and performance of the FPAs and telescope optics are reviewed; telescope performance is exceeding specification in spite of micrometeoroid hits on the primary mirror. The process of image data collection and processing is demonstrated by the iconic “Cosmic Cliffs” image (shown below). The presentation concludes with scientific examples that demonstrate the breadth of JWST capability and glimpse of the science that will be performed over the next two decades.
Language: English
Abstract: TBD
Language: English
Abstract: External environmental conditions lead to thermal deformations of the primary reflector of the 50-m diameter Large Millimeter Telescope Alfonso Serrano (LMT). This talk describes efforts to improve the night-time performance of the telescope at millimeter-wavelengths and allow extension of scientific observations into daylight hours, using the LMT's active surface to counteract the effects of thermal gradients within the antenna structure. Several approaches to stabilizing the LMT’s thermal behavior will be described, including operation of a ventilation system in the antenna backup structure and a real-time metrology system to measure and correct large-scale, thermally induced, surface deformations.
Language: English
Abstract: The Large Millimeter Telescope (LMT) Alfonso Serrano is a bi-national (Mexico and USA) telescope facility constructed on the summit of Sierra Negra, at an altitude of 4600m, in the Mexican state of Puebla. The LMT is a 50-m diameter single-dish radio-telescope designed, constructed and optimized to conduct scientific observations using heterodyne and continuum receivers, as well as VLBI observations, at frequencies between ~70 and 350 GHz. The LMT has an active surface control-system to correct gravitational and thermal deformations of the primary reflector to enable both night-time and daytime observations. We describe the current status and technical performance of the LMT, the instrumentation development program, and an on-going series of engineering and technical upgrades that will increase the optical efficiency and sensitivity of the telescope which will improve the overall scientific productivity and operational efficiency of the LMT.
Language: English
Abstract: Our Milky Way galaxy is unique in that we can obtain the three-dimensional position, velocity and detailed chemical abundances for many individual stars. The massive data sets from long-term spectroscopic surveys and astrometric satellite Gaia, equipped with modern data mining algorithms, have revealed rich structures in the Galactic stellar halo (stellar streams; perturbation from Large Magellanic Cloud) and disk (influence from spiral arms and bar), which hint at the Milky Way's dynamic formation and evolution history. In this talk, I will cover several topics in Galactic dynamics and archaeology, including my recent works: (1) Inference of the dark matter distribution [https://arxiv.org/abs/2012.03908]. (2) Search for disrupted dwarf galaxies [https://arxiv.org/abs/2207.04110]. (3) Analysis of extremely-low-resolution (R=50) Gaia XP spectra to obtain stellar chemistry via machine learning [https://arxiv.org/abs/2404.01269].
Language: English
Abstract: Mass-accreting massive black holes are presumably the most energetic and dynamic sources in the universe, not to mention that they are also an important ingredient of galaxies. However, our understanding of the central engine of active galactic nuclei (AGNs) is mainly limited due to the lack of proper spatial resolution. In this talk I will discuss how we can unveil the structure of black hole engine via time-domain studies. First, I will present a couple of exciting results from the Seoul National University AGN Monitoring Project (SAMP), which was carried out for six years, (2016-2021), and discuss our on-going variability studies for measuring the size of accretion disk and torus. Second, I will discuss the changing-look AGNs, which are currently challenging the orientation-based unification model of AGNs. In particular I will present our new discovery of changing-look AGNs based on the variability characteristic analysis and spectroscopic confirmation.
Language: English
Abstract: Galaxies evolve through the interaction with their surrounding environment. Galaxies are born within the large-scale structure of the universe, and they do not uniformly exist. Consequently, galaxy evolution is expected to differ based on their environment. In fact, in nearby galaxy clusters, it is known that galaxies with similar stellar masses exhibit lower levels of star formation activity compared to typical environments. Conversely, the contribution from galaxies within galaxy clusters or "proto"-clusters to the cosmic star formation rate density rises with increasing redshifts. It is estimated that during the epoch of cosmic reionization, these galaxies could contribute to over 50% of the cosmic star formation rate density. We investigate the reasons behind the low star formation activity in current galaxy clusters and the high star formation activity in high-redshift protoclusters using observations and cosmological galaxy formation simulations. For instance, we discovered that the low star formation activity in galaxies belonging to the Virgo cluster and the Fornax cluster is not due to a decrease in the efficiency of converting molecular gas into stars, but rather because of the lower amount of molecular gas available (Morokuma-Matsui+2021; 2022). In this presentation, I will also introduce our ongoing research on protoclusters at redshifts 6 to 14, utilizing data from a cosmological galaxy formation simulation, FOREVER22 (Yajima+2022).
