I will present recent results on the role of the cosmic web in shaping galaxy properties in the GAMA spectroscopic survey in the redshift range 0.03 < z < 0.25. The stellar mass, u - r dust corrected colour and specific star formation rate (sSFR) of galaxies are analysed as a function of their distances to the 3D cosmic web features, such as nodes, filaments and walls. Significant mass and type/colour gradients are found for the whole population, with more massive and/or passive galaxies being located closer to the filament and wall than their less massive and/or star-forming counterparts. The red fraction of galaxies is found to increase when closing in on nodes, and on filaments regardless of the distance to nodes. Similarly, the star-forming population reddens (or lowers its sSFR) at fixed mass when closing in on filament, implying that some quenching takes place. Comparable trends are also found in the state-of-the-art hydrodynamical simulation HORIZON-AGN. I will argue that these results suggest that on top of stellar mass and large-scale density, the traceless component of the tides from the anisotropic large-scale environment also shapes galactic properties. I will also show that an extension of excursion theory accounting for filamentary tides provides a qualitative explanation in terms of anisotropic assembly bias, and it also explains the absence of type/colour gradients in the data on smaller, non-linear scales.
The Universe evolves hierarchically with small structures merging and falling in to form bigger structures. Due to its proximity, the Local Group (LG) is the best place to witness and study these hierarchical processes in action as evidenced by e.g., the many stellar streams found around the Milky Way (MW) and M31. Stellar systems in the LG have therefore become the benchmark for testing many aspects of cosmological theories. Despite the advances in both observational and theoretical areas in the last decade or so, many fundamental properties (e.g., mass profiles) of the LG and its constituents still remain poorly understood. This is mainly due to the limited information on the transverse motions of stellar systems in the LG. Proper motion (PM) measurements are required to resolve this issue, but this has been technically challenging since the typical motions across the sky are very small. In the past few years, our team has developed a state-of-the-art technique to determine proper motions of resolved stellar systems using multi-epoch HST data. In this talk, I will present results from our HST projects for measuring proper motions of stellar systems in the LG, and discuss how these results are improving our understanding of the LG dynamics.
The second round of large programs is underway at JCMT with nine new science projects. The programs are currently being observed and promise opportunities for expansion to vital multi-wavelength studies. Results of the first large programs are also now being published and will be presented.
90년대 후반 부터 컴퓨터의 계산 성능 향상과 효율적인 수치 알고리즘들의 등장으로 인해 기존에는 제작이 불가능했던 여러 가지 물리 현상들을 영화 및 애니메이션에서 볼 수 있게 되었습니다. 수치해석을 기본으로 하는 이러한 물리 기반 애니메이션 기법은 현재 영화와 애니메이션에서 없어서는 안될 필수적인 요소가 되었습니다. 본 강연에서는 컴퓨터 그래픽스(Computer Graphics)라는 학문 분야와 특수 시각 효과(VFX)라는 산업 분야에 대해서 간략히 소개하고, 이러한 분야들에서 복잡한 물리 현상을 어떻게 구현하여 시각화하는 지에 대해 소개할 예정입니다. 세부 내용으로는 유체(fluid), 강체(rigid body), 변형체(soft body), 옷(cloth), 머리카락/털(hair/fur)들의 사실적인 움직임을 표현하는데에 있어서 물리가 어떻게 활용되는지에 대해서 다루게 될 예정입니다. 또한, 영화나 다큐멘터리에서 우주를 시각화하는 몇 가지 예제들에 대해서도 제작 과정을 함께 보며 여러 가지 생각과 의견을 교환해 보는 자리를 가져보려고 합니다.
Korea has a prodigious history in astronomy. Many astronomical books were published under Sejong the Great, and to our surprise, one of the books recorded that a concentrated alignment of Mercury, Venus, Mars, Jupiter, and Saturn was observed in BC 2467, almost 4500 years ago. Using an astronomical software, we confirmed that this alignment actually happened in BC 2470. The slight difference in time is considered negligible, as it is unclear what kind of calendar was used back then. During the speech, more examples will be given of the ancient observations of the sky, along with how many aspects of traditional Korean culture find their origins in the sky.
Magnetic fields are speculated to affect the collapse dynamics in early star formation to influence the IMF, which may be imprinted in the local metal-poor population. These fields arise by the amplification of primordial fields during the formation of the first (Pop III) and from their feedback. We study the former using MHD simulations with a uniform seed field from cosmological initial conditions to the formation and supernova of a Pop III star. We find that a weak seed field can be amplified to μG at the density peak and by a factor of 100 around the shell of the supernova shock. We also explored the dynamics of metal-poor mini-halos, enriched by Pop III supernova, in varying metallicities and Lyman-Werner flux to produce a fit for the minimum collapse mass. Furthermore, Pop III stars are significant drivers of reionization at high redshift (z > 10). We use semi-numeric methods including Pop III stars as ionizing sources and calculating an optical depth, τe = 0.0569, consistent with the latest results from Planck. The resulting ionization fields can efficiently model the ionizing UV background in cosmological simulations. These results are essential to building a full MHD simulation of the first galaxies.
Water is the most precious resource for sustaining life and enabling exploration. Consequently, until about a decade ago, exploration of the Moon had been limited to space missions and telescopic observations focused on understanding the geology and space environment of the Moon. It was believed the Moon was essentially dry even though there were strong clues for water ice at the poles from ‘enhanced hydrogen’ measurements by orbital neutron spectros measurements and intriguing anomalous radar scattering signatures within a few polar craters that might suggest ice. It was the Indian Space Agency mission, Chandrayaan-1, combined with opportunistic observations by the comet mission, Deep Impact, and the Saturnian mission, Cassini, which made seminal discoveries to fundamentally change our understanding of and raised many more questions about what we now know to be a Moon that does indeed contain significant resources of water. I will discuss some of what has been discovered by these international missions, and what we may learn from upcoming planned and potential missions returning to the Moon including the water ice at the poles, for which there are intriguing theories of origin and evolution. We now also know the illuminated Moon may be ‘hydrated’ with some type of hydroxyl in its surface that may be ephemeral on a diurnal timescale, which is potential evidence for an active process. I will discuss various lines of evidence and theories supporting and arguing against significant hydration on the Moon and will explore the potential of both the confirmed and inferred ‘water’ deposits as possible resources to sustain human and robotic exploration of the surface.
The European Space Agency's Herschel Space Observatory has the largest single mirror ever built for a space telescope. At 3.5-metres in diameter the mirror collects long-wavelength radiation from some of the coldest and most distant objects in the Universe. In addition, Herschel is the only space observatory to cover a spectral range from the far infrared to sub-millimetre. I will present new findings from Herschel.
A thermal imager and spectrometer is being investigated for possible construction in the early operation of the Thirty Meter Telescope (TMT). Combined with the mid-IR adaptive optics (AO) system (MIRAO), the instrument will afford ~15 times higher sensitivity and ~ 4 times better spatial resolution (0.07”) with a greatly improved and stable Strehl ratio at 10um compared to the images delivered by the fast guiding systems of 8m-class telescopes. Through exploiting the large collecting area of the TMT, a high-dispersion spectros mode unrivaled by other ground- and space-based facilities is planned. Such capabilities offer the possibility for breakthrough science, as well as ‘workhorse’ observing modes of imaging and low/moderate spectral resolution. I discuss progress on this instrument concept and especially how it could be used to advance thermal IR observations of AGN.
We present the status of the COsmic BAckground Neutrino Decay search (COBAND) experiment. The signal of the cosmic background neutrino decay is identified as a sharp off at high energy end in a far-infrared region ranging from 15meV to 30meV in the energy spectrum of the photons from the space. The COBAND experiment will be done as rocket and satellite experiments in order to detect the far-infrared photons from the space. For a photon detector of the COBAND experiment, we are developing the Superconducting Tunnel Junction (STJ) detector. We will use a combination of the diffraction grating and the array of Nb/Al-STJ pixels for the rocket experiment, and use Hf-STJ as a micro-calorimeter for the future satellite experiment. The present status of the COBAND experiment is reported in more detail.
The interaction between stars and their surrounding interstellar medium (ISM) is of critical importance for the evolution of galaxies. In this talk, I will present our investigation of the physical properties and excitation mechanisms of the warm molecular gas in the Large Magellanic Cloud (LMC). As a pilot study, we focused on N159W, one of the most active star-forming regions in the LMC, and observed the target with the Herschel SPIRE FTS, detecting CO rotational transitions up to CO(12-11). Our radiative transfer analysis on 10 pc scales revealed the presence of very warm (400 K) and moderately dense (1000 cm-3) molecular gas in the LMC for the first time. In combination with other gas and dust tracers, we examined the observed CO line ratios using state-of-the-art models of photodissociation region (PDR) and shock, finding that mechanical heating by low-velocity shocks, rather than ionizing sources (UV photons, X-rays, and cosmic-rays), is the dominant heating source for CO. Finally, I will the talk by presenting future work, which includes our ongoing investigation of the starbursting 30Doradus region.
The ionosphere is a part of the upper atmosphere (75–1000 km in altitude) where atoms and molecules are ionized appreciably and the propagation of electromagnetic waves is significantly affected by the ionization. Important space weather phenomena such as disruption of communication and navigation systems and damage on power transmission lines are caused by the ionosphere, and therefore, accurate knowledge of ionospheric phenomena and their drivers has a vital importance for the mitigation of the impact of space weather on the society. This talk will provide an overview of ionospheric phenomena and their drivers. In Part 1, ionospheric climatology induced by solar radiation and anomalies associated with electrodynamical coupling of plasma and neutral particles will be introduced. Three key elements for understanding ionospheric phenomena are electric fields, neutral winds, and neutral composition. The physical processes underlying these three elements and their application will be explained in Part 2. Various forms of ionospheric disturbances induced by various sources (geomagnetic storms, plasma instability, tropospheric storms, tornadoes, volcanos, earthquakes, and rocket launches) will be presented in Part 3.