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Abstract: I will review our series of successful programs to dissect the interstellar medium of distant, star-forming galaxies with the Atacama Large Millimeter Array (ALMA). In particular, I will discuss surveys of the set of HI-selected galaxies known as the damped Lya systems (DLAs). We resolve, in part, a decades old struggle to identify the galactic counterparts of these DLAs and thereby place them firmly in the modern picture of galaxy formation. I will also highlight high spectral and spatial resolution observations of the Wolfe Disk, a z~4 galaxy with a Milky Way-like rotation curve.
Abstract: Short and intense transients like gamma-ray bursts (GRBs), and fast radio bursts (FRBs) provide us with irreplaceable laboratories of physics and unique probes of the evolution of the universe. However, observationally obtaining a direct evidence that clarifies the nature of those transients is often difficult due to their short timescale and large distance toward them. In this talk, I will discuss how the origin of GRBs has been unveiled via observationally available clues, and what can we learn about FRBs from the limited information currently available.
Language: English
Abstract: Active Galactic Nucleus (AGN) feedback is widely invoked in galaxy evolutionary models, while evidence of such AGN feedback in action is now observed in the form of galactic outflows. However, the physical mechanism driving AGN feedback remains ill-understood, and whether galactic outflows are powered by jets, winds, or radiation, is still a source of much debate. We consider AGN feedback driven by radiation pressure on dust. We show that such radiative feedback is capable of accounting for the observed dynamics and energetics of galactic outflows, provided that radiation trapping is properly taken into account.
Feedback from the central black hole is usually invoked to quench star formation in galaxies (the standard negative feedback paradigm). We consider the alternative possibility of triggering star formation in the host galaxy, within the feedback-driven outflows (a form of positive feedback). Such "AGN feedback-driven star formation" may contribute to the size and morphological evolution of galaxies over cosmic time. Recently, there has been growing observational evidence for such star formation occurring inside galactic outflows. I will discuss the multiple roles of AGN feedback in galaxy evolution, and how radiative feedback may ultimately shape the co-evolutionary path.
Abstract: 近年の観測機器の目覚ましい発展により、数多くの遠方銀河が検出された。それにより、塵に覆われた爆発的星形成銀河（サブミリ波銀河）、ライマンアルファ輝線を強く放射する銀河（ライマンアルファエミッター）、超巨大ブラックホールを持つ銀河など、宇宙年齢わずか１０億年未満に銀河の多様性がすでに生まれている事が明らかとなった。そして、現在すばるHSC銀河サーベイによって、原始銀河団の候補が多数見つかってきている。初代銀河形成からわずか１０億年の間に、このような銀河の多様性を引き起こしたメカニズムは何だったのか？ そして、原始銀河団のような超高密度領域で銀河進化はどのように進んだのか？ これらを明らかにするため、我々は近年大規模な宇宙論的流体シミュレーションを進めている。結果として、初期宇宙の銀河は超新星爆発のフィードバックにより、星形成が間欠的になること、それにともなって輻射特性も大きく変化する事が分かった。フィードバックによるガスアウトフローとともに、紫外線連続波やライマンアルファ光子は効率良く脱出し、銀河はライマンアルファエミッター・ブロッブとなる。また、原始銀河団領域では、サブミリ波銀河がフィラメント構造にそって複数形成されることが分かった。本講演では、これらのシミュレーション結果について紹介するとともに、銀河とブラックホールの共進化についても議論する。
Abstract: 太陽系にはさまざまな形態の水が広く存在しているが、特に小惑星には、含水鉱物として水が保持されていると考えられている。この含水鉱物は液体の水と無水鉱物が反応して生成されるが、水氷の昇華温度以上でも比較的安定であるため、水の存在を示す重要なトレーサーである。含水鉱物は近赤外線の波長2.7 µm付近に吸収フィーチャーを持つことが知られているが、この波長域は地球大気の吸収のために、地上望遠鏡では観測できていなかった。我々は赤外線天文衛星「あかり」を用いて、地球大気に影響されることなく小惑星の近赤外線分光観測を行い、小惑星66天体のスペクトルを得ることに成功した。その結果、多くのC型小惑星には含水鉱物に起因する顕著な吸収が見られること、一方ほとんどのS型小惑星にはそのような吸収が見られないことがわかった。本講演では、「あかり」による小惑星の近赤外線分光観測の概要とその結果から考えられる小惑星の形成進化過程について紹介し、さらにTAO/MIMIZUKUを用いた世界初の小惑星母天体の内部構造探査計画について議論する。
Abstract: The Juno spacecraft was launched in August of 2011 and was placed into orbit around Jupiter in July of 2016. It is the first solar-powered spacecraft in the outer solar system and the first to be placed into polar orbits. Its primary goals are (1) to determine the O/H ratio from the abundance of water in the atmosphere to discriminate between alternatives for its origin, (2) to understand Jupiter's interior structure and dynamical properties by mapping its gravitational and magnetic fields, (3) to map variations in atmospheric composition, cloud opacity and dynamics to depths of over 100 atmospheres of pressure at all latitudes, and (4) to characterize the 3-dimensional structure of Jupiter's polar magnetosphere and its auroras. Juno is also the first mission to include a public-outreach camera on its instrument payload, which has been providing stunning images of Jupiter at nearly unprecedented spatial resolutions. This talk will survey those results and identify ways in which the general public, as well as space scientists, can become involved in this mission directly.
Abstract: We present cross correlations of the SMARTS optical/infrared and Fermi-LAT gamma-ray light curves for 8 bright blazars that have been monitored with 1 day time bin over the past decade. For the temporal correlation analysis of unevenly sampled variability data, we use the Discrete Correlation Function (DCF), creating an empirical bootstrapping method to assess the significance of the DCF amplitude for each blazar. Our results are perhaps surprising. Early on in the Fermi mission, the brightest gamma-ray blazar 3C 454.3 showed zero lag between optical/infrared and gamma-ray fluxes as reported by Bonning et al. (2012), which was consistent with the leptonic model that optical/infrared photons are produced by synchrotron radiation of relativistic electrons and gamma rays are produced by inverse Compton scattering of ambient photons by the synchrotron-emitting electrons. However, among the 8 blazars, only one blazar ― 3C 454.3 ― shows a significant peak at zero lag, and the other 7 blazars show no significant peak at zero lag. Some blazars show broad peaks at tens of days of lags at or just below 3 sigma significance. In addition, for a given blazar, strong changes of the DCFs from one epoch to the next are shown by the analyses of time periods of one or two year. These results make it complicated to understand blazar emission mechanisms. Possible physical explanations are discussed.
Language: Japanese
Abstract: I will present my recent papers on (i) the luminosity-duration relation of fast radio bursts (FRBs), (ii) ALMA observations of Gamma-Ray Burst (GRB) host galaxies, and (iii) a blue cluster in the local Universe. Brief summaries of each paper are as follows.
(i) Luminosity-duration relation of fast radio bursts We discovered an empirical correlation between luminosity and duration of FRBs. We propose a new distance measure using the relation of FRBs, which can reach more distant Universe than type Ia supernovae in quantity. This method can potentially reveal the time variability of the dark energy, which is one of the central foci of observational cosmology.
(ii) SFRs of two GRB host galaxies at z~2 and a [CII] deficit observed with ALMA We discovered a new parameter to characterize GRB host galaxies, [CII] deficit, by overcoming a serious dust-extinction problem of GRB host galaxies. Possible parameters controlling the deficit include the metallicity, initial mass function, and gas density.
(iii) A young galaxy cluster in the old Universe We discovered a 'blue cluster', that is a local galaxy cluster with an unprecedentedly high fraction of blue star-forming galaxies yet hosted by a massive dark matter halo. The blue cluster challenges the current standard understanding of galaxy formation under the Lambda CDM Universe.
Language: English
Abstract: Cool-core clusters of galaxies were originally predicted to form massive (~10^2 - 10^3 Msun/yr) cooling flows as the intracluster medium (ICM) radiatively dissipates thermal energy and descends the gravitational potential well of the cluster. However, mechanical mode feedback from the active galactic nuclei (AGN) of the brightest cluster galaxies (BCGs) in cool-core clusters has sufficient energy to offset cooling in the core, and suppresses cooling flows. Residual ICM condensation gives rise to spectacular starbursts in the normally "red-and-dead" BCG and cold molecular gas reservoirs that can be several 10^10 Msun, and observations of condensed material provides important clues for how feedback moderates cooling in galaxy clusters. In this talk, I will focus on our observations of star formation and condensed material in the CLASH (Cluster Lensing And Supernova survey with Hubble) sample of galaxy clusters, with particular focus on our recent study of dust and molecular gas in the BCG of MACS 1931.8-2635 conducted with ALMA. MACS 1931 hosts one of the most extreme BCG starbursts known in a cool-core cluster, with a star formation rate of ~250 Msun/yr, and multiphase gas filaments extending ~30 kpc from the center of the BCG. Our observations in MACS 1931 reveal a massive (~2 x 10^10 Msun) molecular gas reservoir that is highly excited (R_31 = 0.93 +/- 0.16), suggesting that gas excitation is being partially driven by non-photodissociation region- related processes, while continuum observations of dust allow us to constrain the temperature of several dust clumps to <10 K, which is too cold to be directly interacting with the surrounding ~4.8 keV intracluster medium (ICM). Excitingly, our findings imply a scenario where BCG dust, which is not predicted to survive on longer than Myr timescales in hot ICM environments, can be shielded from ICM sputtering. I conclude by discussing how observations like our observation of MACS 1931 constrain the formation and evolution of dust and gas in the extreme feedback-regulated environments of cool-core clusters.
要旨： 星間空間に多大な影響を及ぼし銀河進化を規定する大質量星の形成条件を探るためにはその主たる前駆体である巨大分子雲の理解が重要となる。これまでは分子雲を空間分解した観測は単一電波望遠鏡による銀河系内の分子雲のみに限定されてきたが、ALMAの登場により星形成の直接母体となる分子雲コア/クランプ(数pc~0.1pc)を空間分解可能な観測は系外銀河(大小マゼラン雲やM33)の分子雲に拡大されつつある。これらの観測は、視線方向上の重なりを考慮する必要がほとんどないことに加えて、金属量による違いや銀河スケールの構造/現象による星形成への影響を調べる上でも重要であり、宇宙進化史における星形成の一般的な理解に向けてさらなる飛躍をもたらすと期待される。
本講演では主に、ALMAによる0.”2(～0.07 pc)の高分解能観測によって得られた大マゼラン雲N159領域の結果について紹介する。EとW領域にて、~0.1 pc 幅のフィラメント状分子雲と大質量原始星からのアウトフロー、わし座で見られる”創造の柱”構造などを系外銀河の分子雲で初めて同定した。この2つの領域は互いに 50 pc以上離れているにも関わらず、非常に似た性質/進化段階を示すことから、銀河規模の大局的なガスフローが同時多発的なフィラメント状分子雲/大質量星形成に重要な役割を果たしたと考えられる。
この他マゼラン雲やM33に対するALMAを用いた観測の進行状況を簡単に紹介し、今後の展望について議論する。
Language: Japanese
Abstract: Polarization anisotropies on the cosmic microwave background (CMB) is an interesting target for cosmology. Especially, the parity-odd component, the so-called B-mode, in degree scale is a unique probe of primordial gravitational waves from the cosmic inflation. The POLARBEAR experiment is a ground-based CMB polarization measurement at the Atacama Desert in Chile with 1,274 transition-edge-sensor (TES) bolometers sensitive to the 150 GHz band on a 2.5 m aperture off-axis Gregorian type telescope. Since 2014, POLARBEAR has started observations of a 670 square degree patch of the sky using a continuously rotating half-wave plate, which is located at the prime focus to suppress the detector noise below ~0.1 Hz by modulating polarization signal. In this talk, I present the characterization of the instruments including studies about detector nonlinearities and atmospheric clouds. Then, I report the result of the B-mode angular power spectrum measurement.
Abstract: The discovery of thousands of planets around stars other than our Sun has revived age-old questions on how these exo-planets form and which chemical ingredients are available to build them. Star formation and chemistry start in the cold and tenuous clouds between the stars. New facilities such as ALMA allow us to zoom in on dense cloud cores and planetary system construction sites with unprecedented sharpness and sensitivity. Spectral scans of young disks contain tens of thousands of rotational lines, revealing water and a surprisingly rich variety of organic materials, including simple sugars and high abundances of deuterated species. Yet more mature protoplanetary disks show very few lines. How are these molecules formed and what chemical and physical processes play a role? How common are they? And how do they compare with the inventory in comets such as come 67P/C-G?
Abstract: I will talk about two topics related to spectroscopic studies of quasars and stars in the optical and near-infrared regions:
(1) Quasar elemental abundances are expected to provide unique probes of high-redshift star formation and galaxy formation. Using the archival optical spectra of SDSS quasars at 0.7 < z < 1.6, we measured Fe II and Mg II emission-line strengths and estimated [Mg/Fe] abundance ratios from them in combination with photoionization simulations. The derived abundance ratios are consistent with chemical evolution models, which validates our abundance estimate. However, because chemical evolution models are degenerated at 0.7 < z < 1.6 regardless of the star formation history, we could not put any strong constraints on it. Future observations with the forthcoming TAO instruments (NICE, SWIMS) would shed light on the evolution of [Mg/Fe] abundance ratio at 3 < z < 7.
(2) WINERED is a near-infrared high-resolution echelle spectrograph that simultaneously covers the wavelength range of 0.91-1.35 micron with a resolving power of ~28000 (WIDE mode). As a member of the WINERED team, I have tackled correction of an observed spectrum for telluric absorption, which is an unavoidable problem for ground-based telescopes. We succeeded to correct telluric absorption with high accuracy by using the spectrum of a telluric standard star whose stellar features were carefully removed. By applying this method to a spectrum of the A-type star 21 Lyn obtained with WINERED, we identified 219 atomic lines. Intriguingly, a curve of growth created from the measured C I lines showed large scattering that cannot be explained by measurement errors. This result, combined with other near-infrared spectroscopic studies, implies that not a few of oscillator strengths of near-infrared lines need calibrations based on astronomical observation.
Language: slides in English, talk in Japanese
要旨:
科学論文の英文校閲の現場で遭遇する多種多様な問題の中で、修正する箇所として最も多いのは、ほぼ例外なく冠詞と可算非可算、単数複数の用法です。筆者が相当の英語上級者であっても、いやむしろあればこそ、割合的にその点が頻出修正事項になります。不幸なことに、冠詞と名詞の単複ほど本質的に校閲が難しい点はありません。なぜならば、基本的な誤りでない限り、文法的にはどちらでも正当であることが普通だからです。
しかし、いかに文法的に正しくても、冠詞と単複を誤ると、文意が筆者の意図と大きく異なってしまうことがままあります。正確さと精密さとが命の科学論文においては、書く場合はもちろん読む場合でさえ、これは致命的になりかねません。そんな時、文法的には正しい以上、読者が読み取る判断の拠り所は、文章の背景知識に基づいた「常識」だけになります。ところが、例えば「太陽は1個」が世の常識であっても、天文屋の常識は異なることもありましょう。あるいは自ら開発した装置の「常識」を読者に要求するのは無理難題というものです。究極的には、筆者の意図に沿った「正しい」冠詞や単複は、筆者にしか説明できないものなのです。
本講演では、自身かつては天文学研究者であり、近年は一流の天体物理論文の校閲を数多く請負った講演者により、日本人科学者による誤用の実例も使いながら、英語の冠詞と数詞のテーマに構造的に切り込みます。日本語ネイティブならではの視点から、実用的な対策も提案します。
