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Abstract: One of the most fundamental questions in galaxy formation and evolution is to understanding the establishment of the Hubble sequence, particularly how blue, star-forming galaxies are transformed into red, quiescent galaxies. In this talk I will present some new insights into this question based on recent observational results at high redshift, primarily at z > 2, and discuss how star-formation is regulated and quenched in massive galaxies and what are the possible roles of environment and supermassive black holes in this process. Specifically, I will show how ALMA unveils a significant population of promising progenitors of the earliest-quenched galaxies at z~4, and how we captured the onset of environmental effects on massive galaxy evolution in the most distant galaxy clusters at z=2.5.
Language: English
Abstract: The two Magellan 6.5 meter telescopes were designed, constructed and are currently being operated at Las Campanas Observatory in Chile by a consortium of US universities and research institutions. This talk discusses some of the thinking that went into their design, notable features, and the transport of the telescope to the observatory and installation on site. The talk concludes with the results of some recent investigations of seismic performance.
Language: English
Abstract: 太陽のおよそ１０倍より重い星は進化の果てに中心に鉄コアを作る。その鉄コアが自身の重力で潰れることから始まる現象が重力崩壊型の超新星爆発である。中心部にはパルサーの元となる原始中性子星が形成され、超新星爆発ではその外側の吹き飛ばされた部分が光る。この中心部の密度、温度は極限的に高くなり、弱い相互作用でしか生まれない粒子であるニュートリノが効率的に放出される。実際、このニュートリノがまさに外側の物質を吹き飛ばすのに一役買い、これをニュートリノによる加熱機構と呼ぶ。この超新星爆発の計算は非常に難しく、安定かつ信頼できる枠組みでシミュレーションできるようになったのは２０００年代の前半である。しかし、その結果は驚くべきことに、爆発が起こらないというものであった。何が問題なのだろうか？実は、それらの計算では簡単のため、球対称という仮定を課しており、対流の効果が入っていなかった。我々はそれを取り除き、３次元計算することで、超新星爆発が成功するという結果を得た。３次元計算することで、ニュートリノや重力波の放出も議論できるようになり、超新星爆発のシミュレーション結果を将来の観測と比較できるような時代がついに訪れる。今回のセミナーでは、超新星爆発の機構から最近の研究までをレビューする。超新星爆発の研究の新時代の到来を感じていただければ幸いである。
Language: Japanese
Abstract: I will overview the young neutron-star model for fast radio bursts (FRBs). Applying the model to a repeating FRB 121102, which has been recently identified as a cosmological event, I will discuss the possible progenitor systems.
Language: English
Abstract: In the Local Group, there are several tens of dwarf galaxies, which have sub-solar metallicity. They provide us a great opportunity to constitute a basic template to study faint low-metallicity galaxies, such as those at high redshift. Because metallicity is an important parameter which significantly affects gas-phase and grain surface chemistry, chemical compositions of molecular clouds in low-metallicity dwarf galaxies are of great interest. To investigate the chemical composition in low-metallicity environments, we have conducted spectral line survey observation in the 3 mm band (85-116 GHz) toward low-metallicity dwarf galaxies, the Large Magellanic Cloud, IC10, and NGC6822. The lines of CCH, HCN, HCO+, HNC, CS, SO, 13CO, and 12CO have been detected. The spectral intensity patterns are found to be similar among three dwarf galaxies. Compared with solar-metallicity environments, the chemical compositions of dwarf galaxies are characterized by deficient nitrogen-bearing molecules, as a direct effect of the lower elemental abundance of nitrogen, and abundant CCH and deficient CH3OH, as an effect of extended photon dominated regions in cloud peripheries due to the lower abundance of dust grains.
Language: Japanese
Abstract: Constraining the grain size in protoplanetary disks is a key to understand the first stage of planet formation. The grain size has been estimated by measuring the spectral index at millimeter wavelengths, while it has huge uncertainties. Here, we propose that millimeter-wave polarization is another method to constrain the grain size. We show that thermal dust emission is scattered off of other dust grains and the residual polarization is up to 2.5 %, which is detectable with ALMA. This self-scattering polarization is efficient only if the maximum grain size is comparable to the wavelengths. Therefore, we can constrain the grain size from millimeter-wave polarization of protoplanetary disks. Furthermore, we have observed the protoplanetary disk around HD 142527 with ALMA polarization mode, and found the evidence of the self-scattering plays a role in the protoplanetary disk.
Language: Japanese (slides in English)
Abstract: 2015年にaLIGOの観測が始まり、その中で重力波の初検出が達成されその観測期間中には計２つの重力波が検出された。どちらも連星ブラックホールの合体であった。またつい先日に、２０１７年１月４日に３つ目の連星ブラックホールの合体による重力波観測が報告され、周辺分野をにぎわわせている。今後はそういった観測の天文学的な情報を得るために、仏伊のadVirgo、KAGRAといった重力波望遠鏡ネットワークで観測を行う体制、そして重力波望遠鏡のみでは非常に困難な、重力波源の特定を実現するために様々な波長での天文観測の連携体制が望まれている。本講演では、現在の重力波望遠鏡の観測結果と、各望遠鏡の現状を報告する。また、検出した重力波からどんな物理が引き出せるかという問題について、超新星爆発からの重力波検出を例にその試みの一端を報告したい。
Language: Japanese
