![[PukiWiki]](image/pukiwiki.png "[PukiWiki]")
Language: English
Abstract: We investigate the connection between the galaxy and their dark matter halos and how it evolves with time. Utilizing the excellent depth of the Subaru Hyper Suprime Cam Survey (HSC), we measure the masses of dark matter halos which host HSC galaxies using the technique of weak gravitational lensing. We bin galaxies in variety of stellar mass threshold bins ranging from log M*/(h^-2 Msun = 8.6 to 11.2 in two redshift bins z=[0.3, 0.55] and [0.55, 0.8] and analyse the weak lensing signals in the context of the halo occupation distribution model to infer the scaling relation between stellar mass of galaxies and their halo mass. We present how systematics involved in the measurements of the weak lensing signal, especially due to the use of lens galaxies with photometric redshifts, can affect this inference. If time permits I will also present our efforts to test models of galaxy assembly bias using the HSC weak lensing signals of galaxies from DESI.
Language: Japanese
要旨: 観測天文学において、減光は避けられない事象であり、その補正は永遠の命題と言える。しかしながら、ともすると減光は目標天体の「前景」の問題と捉えられ、減光補正は目標天体の解析とは切り離されて扱われる傾向にある。ところが、輝線天体の減光量を正しく見積るには、目標天体輝線ガスの物理状態を知る必要がある。従い、実際には減光補正とプラズマ解析は包括的に行って無矛盾最適解を求める必要がある。しかし、先行研究を紐解くと、無矛盾最適解を厳密に追求するケースは期待に反して多くはない。
一般的な減光則を用いて輝線天体分光データを補正する場合、標準波長（一般的には水素バルマーβ輝線）の青側・赤側で逆センスの補正になる。そのため、プラズマ診断で用いる輝線が標準波長の両側にまたがって分布している場合、減光量見積りの精度がプラズマ診断の精度に如実に影響を与えることになる。日常的に多波長分光データを扱うようになった昨今、これは由々しき問題になりかねない。
そこで我々は、最低5本の水素再結合線を検知できれば、目標輝線天体の分光データから、目標天体視線方向の減光量（c(Hβ); 天体周辺、星間、銀河間由来すべて含む）と規格化された選択減光（Rv）、並びに、目標天体輝線ガスの電子温度（Te）と電子密度（ne）を一括同定する方法を開発した。ここに提案する方法では、減光補正とプラズマ解析の相互依存性からc(Hβ)とRvをTeとneの関数と表すことにより、減光補正とプラズマ解析の無矛盾最適解を求めることが可能となる。特に、自家分光データのみから目標天体視線方向のRv値をも求められる、という点は画期的である。
ランダムモデルを用いた検証により、輝線強度の観測精度が数%の場合、c(Hβ)とRvは10%程度、Teは数%の精度で解が求められることが示された。neの精度は、水素輝線がそもそも電子密度にセンシティブな輝線ではないために劣るが、この方法で決まるTeと他の密度診断輝線によるプラズマ解析を組み合わせれば、数%の精度で求められる。この新手法は、惑星状星雲のプラズマ解析精度の向上を動機として開発されたが、得られる輝線が少ないような暗い遠方の輝線天体にこそ有益な手法と思われるため、この機会に紹介させていただきたい。
この研究は2023年度の国立天文台(大学支援経費)「委託研究」事業の支援を受けて行われている。
Language: Japanese
要旨: 極地や高山に分布する積雪や氷河，永久凍土は，低温で過酷な環境であるため長く生物は生息できない場所と考えられてきた．しかし，このような環境にも，近年多様な生物が生息していることがわかってきた．例えば，昆虫やミジンコ，ミミズ，クマムシなどの無脊椎動物，光合成を行う藻類，さらに生物の遺骸や有機物を分解するバクテリアなどである．これらの生物は，低温環境に特化した進化を遂げ，雪氷生物として知られている．雪氷生物は，互いに補食被食の関係を持ち，積雪や氷河に独立した生態系を作っている．また，雪氷生物の繁殖は，雪氷の表面のアルベド（反射率）を変化させることで，氷河や積雪の融解を加速する効果をもつこともわかってきた．分子生物学，特にゲノム解析の進歩により，これら低温環境に生息する微生物の多様性や，微生物がもつ特殊な機能が明らかにされつつある．雪氷生物と雪氷圏との相互作用は，全球スケールの気候変動や地球生命史においても新しい視点を提供する．さらに，氷河や永久凍土などの雪氷環境は，太陽系の他の天体にも存在するため，雪氷生物は地球外生命の存在を探る上でのモデル生物としても期待されている．
Abstract: Glaciers, snowpacks, and permafrost in polar and alpine areas have been believed to be lifeless environment for a long time. However, diverse organisms have recently been found to live there across the world. For example, invertebrates such as insects, copepods, iceworms, and water bears, photosynthetic microbes such as snow algae, and heterotrophic bacteria are living in snow and ice. They are special species adapted to cold environment and form simple and closed ecosystems in the cryosphere. As their blooming on glaciers and snowpacks can reduce albedo of snow and ice and enhance their melting, they have a strong impact on cryosphere and global climate. Recent advance of genomic analyses of the organisms has revealed their diversity and special physiologic functions. As glaciers and permafrost can widely be found in other planets in our solar system, they are the best model organisms to explore extra-terrestrial life.
Language: Japanese
Abstract: MWとM83を例として、近傍銀河の銀河構造と分子ガスや分子雲の進化について話す予定です。特に、分子ガスや分子雲の寿命や、「分子雲パラダイム」の限界について、最近の動向や私たちのグループの研究成果（あるいはまだ成果とまでは言えず考え中の部分）も含めて話します。銀河内部でのガスの運動が、重力的に束縛された分子雲としてN-body的なものか、それとも広がった連続流体的なものか、あるいはその中間か、はガス進化の結果として起きる星形成や銀河進化にも重要な問題です。 そういう問題意識で聞いてもらうと、興味もっていただけるかなと思います。それからせっかく卒業校である東大センターで話すので、学生時代に習った「自分の頭で考えるように」とか「物理的に考察するように」とか、実際に身に沁みて重要だと思う、という偉そうなこともちょっと言うかも。
Language: Japanese
Abstract: ちゃんとした英語文章を書くとき、自分の英語が本当に意図通り伝わるのか、不安感がなかなか拭えない経験がありませんか。母国語でさえ書き言葉は難しいところ、英語ならばなおさらなのはもっともです。その時、明日からでも実行できる最大の対策は、理路整然と書くことにつきます。それは論文であれあるいは交渉事の通信であれ共通の大原則です。
近年はChatGPTなどAIベースの優れたツールも登場してきました。しかし、元々筋が間違っていたりあるいは入り組んでしまっている文章を正確で読みやすいものにしてもらうことは期待できません。実はAI時代だからこそ、今まで以上に書き手の資質が問われるとも言えます。むしろ、AI生成の十把一絡げの文章があふれかねない近未来こそ、書き手として何か光るものを出したいものです。
本講演では、理路整然とした筋の立て方と、それを英文として確実に伝達する作文方法について、本質的でかつ具体的、実戦的なアドバイスをまとめます。近年の補助ツールの発展の功罪にも触れます。過去データ機械学習をベースとするAIに特有の欠点であるコンプライアンス的問題についても言及し、グローバル時代を生きる人々のコミュニケーションに一つの指針を提供します。英国在住20年超、論文他の英文校閲を主業とし、日本語を母語とする理系研究者や学生の英文に見られる典型的傾向を熟知する講演者によるセミナーです。
Language: English
Abstract: The evolution of galaxies is directly linked to the gas reservoirs surrounding them, so-called, "the circum-galactic medium (CGM)". Gas and metals are exchanged via inflows and outflows through the CGM, which is an interface between the interstellar medium (i.e., galaxy) and intergalactic medium (the rest of the Universe). The CGM has been studied with absorption lines imprinted in spectra of bright background quasars (tomography), but this method is limited to line of sight and cannot provide the 2D spatial distribution of the CGM. Recent sensitive, wide-FoV integral-field spectrographs (such as VLT/MUSE and Keck/KCWI) make it possible to individually detect the CGM in emission, which allows us to map the gas and metals around host galaxies. In this talk, I will review the recent progress of observations and understanding of hydrogen gas and metals around z>~2 galaxies, which are detected as extended Lyα emission (Lyα haloes) and metal-line haloes. I will also bridge the CGM observations in emission and absorption and introduce comparisons with simulations.
Language: Japanese
Abstract: ミリ波・サブミリ波(35– 950GHz)帯の巨大電波望遠鏡であるアルマ望遠鏡は、 2013年の本格運用開始以来、銀河や星・惑星系の形成の現場などを、従来にない 高感度と高解像度で描き出してきた。また長波長(50MHz – 15GHz)帯の次世代 大型電波望遠鏡としてSquare Kilometre Array (SKA) の建設が開始されている。 SKAでは宇宙初期の天体形成の解明や重力理論の検証など、この波長でなければ 達成できない科学目標に挑む。
電波天文観測システムは、情報通信技術の進展を背景に新しい段階を迎えている。 本談話会ではアルマおよびSKAを実例として、電波天文観測システムと情報通信 技術の関係について俯瞰する。また、近年のソフトウェア無線 (SDR : Software Defined Radio) の発展により実現可能となった、安価で手軽な機器を用いた 電波天体観測の実例も紹介する予定である。
Language: Japanese
Abstract: Gravitational microlensing has a unique strength in its sensitivity to planets with masses as low as Earth mass just beyond the snow line, where the core accretion theory of planetary formation predicts the most efficient planet formation. Because it does not rely on the light from the host star, microlensing can detect the planets orbiting around faint stars such as M-dwarfs and brown dwarfs, as well as free-floating planets, and black holes. So far, about 250 exoplanets were found by this method thanks to survey observations by MOA (Microlensing Observations in Astrophysics), OGLE (Optical Gravitational Lensing Experiment) and KMT-Net (Korean Microlensing Telescope Network) groups. In this talk, I will present recent results provided by microlensing observations. I will also talk about the PRIME (PRime-focus Infrared Microlensing Experiments) project, which has recently started survey observations towards the Galactic center in infrared in South Africa.
Language: English
Abstract: This talk will present first results of the MIRI-MRS spectra of a number of protostars, T Tauri and brown dwarf disks resulting from the JOYS and MINDS GTO programs as well as a number of open time programs. Rich ice spectra are seen in dark clouds and the cold outer envelopes of protostars hinting at the presence of complex molecules in ices formed very early in the evolution. In young and mature disks, many lines from gaseous CO, H2O, CO2, C2H2 and HCN are found, but also surprising new molecules are detected. Together they point to a rich chemistry that is linked to the physical structure of the inner regions of these disks and thereby provides a unique diagnostic of it. Background information: the 55 hr JWST Observations of Young protoStars (JOYS) GTO program (PI: van Dishoeck) uses MIRI to investigate the physical and chemical properties of two dozen protostars and their immediate environment. JOYS studies the physical characteristics of embedded disks, accretion signatures onto the protostars, feedback from the young protostars on their environment through primordial jets and outflows, as well as the chemical gas and ice constituents of the protostellar envelopes to feed the disks. The goal of the 120 hr MIRI Mid INfrared Disk Survey (MINDS) GTO program (Th. Henning, I. Kamp co-PIs) is to use JWST to (1) investigate the chemical inventory of the terrestrial planet forming zone, (2) to follow the gas evolution into the disk dispersal stage, and to (3) study the structure of protoplanetary and debris disks in the thermal mid-IR. The program builds a bridge between the chemical inventory of planet-forming disks and the properties of exoplanets. In total, about 50 targets (Herbig Ae stars, T Tauri stars, brown dwarfs and young debris disks) are being observed.
Language: Japanese
Abstract: Chemical composition around young stellar objects (YSOs) is an essential tool to investigate physical conditions and the history of star formation. Approximately 300 molecules have been detected in the interstellar medium so far. Some of them are categorized into complex organic molecules (COMs), and others are called carbon-chain molecules, which account for ~40% of the interstellar molecules. In this talk, I will present our recent work on chemistry on COMs and carbon-chain species around massive YSOs using ALMA. One topic is a study to investigate the formation processes of NH2CHO, a possible prebiotic molecule, using the ALMA Band 6 data toward 30 high-mass star-forming regions called the DIHCA project. Another topic is research to investigate chemical differentiation among carbon-chain species and nitrogen- and oxygen-bearing COMs using ALMA Band 3 data. We have proposed new carbon-chain chemistry around massive YSOs which we name Hot Carbon-Chain Chemistry (HCCC).
Language: Japanese
Abstract: The mystery of the fast-rotating atmosphere on Venus is well known as the name of the super-rotation. At the cloud top altitude of ~70 km, the super-rotation reaches 100 ms-1 and many types of atmospheric waves are found as periodical signals in winds and temperatures. Planetary-scale waves are one of the important clues that maintain the super-rotation by transporting angular momentum and heat. Imai et al. [2016] implemented long-term monitoring of the rotation period of planetary-scale UV features using a ground-based telescope. Two significant periodicities, at 5.1 and 3.5 days, should be manifestations of these planetary-scale waves (Rossby wave and Kelvin wave, respectively), which were subjected to temporal variations within several months. However, the temporal evolution of these variations remained largely unknown. On 7 December 2015, the Japanese Venus Climate Orbiter named Akatsuki successfully inserted the Venus orbit, and its exploration is still ongoing. The periodicities in the UV brightness and winds derived from cloud-tracking were analyzed throughout the entire observation, and dramatic evolutions of planetary-scale waves were revealed [Imai et al., 2019]. One of the prominent events was observed from June to October 2017, where a 5-day Rossby wave consisting of equatorially symmetric planetary-scale vortices with zonal wavenumber 1 had been captured. At the same time, planetary-scale temperature deviations associated with the 5-day wave were reconstructed for the first time from the Longwave Infrared Camera (LIR) images. By using cloud-tracked winds and brightness temperature measurements, angular momentum and heat fluxes induced by the 5-day wave were quantitatively estimated. While the origin of transient waves is still unclear, the poleward heat transport suggests that they can be related to upward propagating Rossby waves and/or baroclinic instability waves in the lower cloud layer. In this talk, I would like to introduce our research with the "history" of myself involved in planetary exploration missions based on my background in ground-based observations.
Language: Japanese
Abstract: Machine learning has been successfully applied in varied field but whether it is a viable tool for determining the distance to molecular clouds in the Galaxy is an open question. In the Galaxy, the kinematic distance is commonly employed as the distance to a molecular cloud. However, there is a problem in that for the inner Galaxy, two different solutions, the “Near" solution, and the “Far" solution, can be derived simultaneously. We attempted to construct a two-class ( “Near” or “Far” ) inference model using a Convolutional Neural Network (CNN), a form of deep learning that can capture spatial features generally. In this study, we used the CO dataset toward the 1st quadrant of the Galactic plane obtained with the Nobeyama 45-m radio telescope (l = 62-10 degree, |b| < 1 degree). In the model, we applied the three-dimensional distribution (position-position-velocity) of the 12CO (J=1-0) emissions as the main input. The dataset with “Near” or “Far” annotation was made from the HII region catalog of the infrared astronomy satellite WISE to train the model. As a result, we could construct a CNN model with a 76% accuracy rate on the training dataset. By using the model, we determined the distance to molecular clouds identified by the CLUMPFIND algorithm. We found that the mass of the molecular clouds with a distance of < 16.3 kpc identified in the 12CO data follows a power-law distribution with an index of about from -1.5 to -2.3 in the mass range of M >1000 Msun. In particular, the slope was shallow in the arm region and the bar-end region. Also, the detailed molecular gas distribution of the Galaxy as seen from the Galactic North pole was determined. In addition, we obtained a result that approximately 450 cloud-cloud collision events are expected to be included in the data.
Language: English
Abstract: The discovery of complex organic molecules (COMs) in solar-type protostars highlights the extensive chemical evolution at the onset of planet formation. These molecules, which are potential precursors to pre-biotic molecules, are also found in comets that contain the most pristine matter in the solar system. In recent years, the increasing detection of COMs by interferometric sub-mm/mm observations, such as ALMA and VLA, suggest a common presence of COMs in the early stage of star formation. However, the formation pathways of COMs and whether most protostars undergo similar chemical evolution remain open questions with incomplete observational constraints. It is thought that COMs form in the ice mantles on dust grains followed by thermal sublimation near protostars, but direct observational constraints are scarce. While ALMA provides sub-100 au resolution, a resolution necessary to resolve sites of planet formation, to characterize gaseous COMs in nearby embedded protostars, measurements of chemical composition in ices had been limited by low-resolution and limited sensitivity spectroscopy until JWST, which can probe ices at a spatial scale comparable to that by ALMA with unprecedented sensitivity. In this talk, I will highlight the frontier of complex chemistry from observations of COMs in both gas- and ice-phase. Particularly, I will discuss the recent JWST results on ice in protostellar environments, especially focusing on the latest results of the CORINOS program. We have found potential signatures of icy COMs in a young embedded protostar. I will also discuss the prospects of a holistic chemical analysis of both ice and gas in the era of JWST and ALMA.
Language: English
Abstract: The James Clerk Maxwell Telescope (JCMT) has been monitoring eight nearby low-mass star-forming regions in the Gould Belt at submillimetre wavelengths for over six years to search for and quantify the time dependent brightness variability of the resident deeply embedded protostars. Secular variability is common among these protostars; greater than 25% of the sample show measurable long-term brightness changes and 10% show burst behaviour lasting months to years. We interpret this secular variability as reflecting changes in the mass accretion rate from the disk to the protostar, as predicted by theoretical models of (proto)stellar assembly. For a subset of our sample we have contemporaneous mid-IR light-curves which allow additional constraints on the conditions responsible for the brightness variations, confirming that the submillimetre variability is driven by changes in the dust temperature profile of the envelope. Furthermore, we have combined, for one source, single dish and interferometric sub-mm monitoring, which has allowed us to unambiguously recover a time lag in the variability at larger angular scales and use the results to confirm the envelope structure surrounding the embedded protostar. More recently, we have added somewhat more distant intermediate mass regions to our JCMT monitoring and collaborated with the Maser Monitoring Organization (M2O) in follow-up of more massive protostar candidate variables.
