March 26 Tue 10:00-11:30
太陽系小天体セミナー
Zoom
March 27 Wed 15:30-16:30
NAOJ Science Colloquium
hybrid; Lecture room and Zoom
詳細は下記からご覧ください。
=============== March 26 Tue===============
キャンパス：三鷹
セミナー名：太陽系小天体セミナー
定例・臨時の別：定例
日時：3月26日（火曜日）10時00分～11時30分
場所：zoom
講演者：春日敏測
タイトル：DARTによる科学成果とSubaru HSCに期待される太陽系小天体研究
Abstract：DARTミッション(Double Asteroid Redirection Test)は,
NASAが地球防衛のために実施した探査/実験プロジェクト.
二重小惑星システムDidymos-Dimorphosを対象に, 2022年9月26日UTに探査機を衛星Dimorphosに衝突させ,
その軌道を逸らすテストを実施した. 運動量増強係数βは3.61(1σ: +0.19,
-0.25)と見積もられ,数値計算や地上衝突実験による予測値(β=1~6)の範囲内であった.
衛星Dimorphosの公転周期は33±1分短縮され, 軌道長半径は1.21kmから1.17kmへと短くなった.
衝突によって放出されたダストの総質量は~1e7 kg, その大部分を占めたのはboulder
swarmsを含むslow-moving ejecta (>99.5%)であった. 一時的にダブルトレイル構造が観測されたが,
衝突以外のダスト放出メカニズムは確認されず, その見かけは円錐状のイジェクタカ
ーテンに起因する可能性が指摘された. 実際に衝突時以外には衛星Dimorphosの散乱断面積の増大は観測されていない.
DARTミッションにより小惑星軌道変更技術の有効性が実証された. Subaru Hyper Suprime-Cam
(HSC)のデータを用いた既知太陽系小天体の抽出と同定手法は確立されつつある(大坪貴文氏(産業医科大)).
HSCデータから収集された小天体情報は,Minor Planet CenterやNASA/JPL
HORIZONSでの位置情報/観測条件と併せることで軌道情報を取得できる.
各CCDの視野内に小惑星が収まっているかどうかを計算することで効率的な検索アルゴリズムの実装に成功している.
今後は潜在的な地球衝突危険天体の早期発見と追跡にも活用でき,
地球防衛に向けて将来的な小惑星衝突リスク軽減への貢献が期待される.
Refs: DART (Cheng et al. 2023, Nature; Graykowski et al. 2023, Nature; Jewitt et al. 2023, ApJL; Kim & Jewitt 2023, ApJ; Li et al. 2023, Nature; Moreno et al. 2023, PSJ; Thomas et al. 2023, Nature; etc…)
世話人の連絡先
名前：渡部潤一
備考：テレビ会議またはスカイプによる参加も可
=============== March 27 Wed===============
Campus: Mitaka
Seminar: NAOJ Science Colloquium
Date and time: 2023 Mar. 27 (Wed.), 15:30-16:30
Place: the lecture room / Zoom (hybrid)
Speaker: Laia Barrufet
Affiliation: The University of Edinburgh
Title: HST-dark galaxies: Unveiling the Nature of Infrared Bright, Optically Dark Galaxies with Early JWST Imaging and Spectroscopy
Abstract:
Over the past decade, low-resolution infrared observations have revealed a population of bright IR galaxies undetected with HST, termed “HST-dark galaxies. Nevertheless, their photometric redshifts and physical properties were uncertain due to the limited photometry even including ALMA data. This can result in an incomplete galaxy census at earlier times, due to UV-faint galaxy populations such as quiescent or dust-obscured sources. The key question is: how common are such sources at z >3-4 and what is their contribution to the cosmic star formation rate density? With JWST, we can study for the first time the physical properties of this enigmatic population. In this talk, I will summarise the progress in our understanding of HST-dark galaxies facilitated by JWST data, employing both photometry and spectroscopy. In the first part of the talk, I will expose the progress made with HST-dark galaxies thanks to JWST/NIRcam photometry. I will focus on the results of 30 HST-dark sources selected based on their red colours across 1.6 to 4.4 microns with NIRCam imaging from the Early Release Science Program CEERS. These galaxies are generally highly dust-attenuated, massive, star-forming sources at z~2-8. Our analysis underscores the unique capability of JWST in uncovering this previously elusive galaxy population and in conducting a more complete census of galaxies at z>3 based on rest-frame optical imaging. Interestingly, HST-dark galaxies present a considerable contribution to the obscured star formation rate density at z~7, already in the Epoch of Reionization. In the second part of the talk, I will present the initial NIRSpec spectra of HST-dark galaxies from my GO Cycle-1 program ‘Quiescent or dusty? Unveiling the nature of extremely red galaxies at z>3’. I will showcase spectra for highly attenuated dusty galaxies and quiescent galaxies and their physical characteristics. Despite the prevalence of dust in most galaxies, they exhibit distinct spectral features. Furthermore, HST-dark galaxies harbour hidden gems: quiescent galaxies at redshifts > 3, for which I will present spectra and demonstrate NIRSpec’s capacity to analyze these sources. Finally, I will explore potential avenues for future research involving HST-dark galaxies, leveraging the synergy between JWST and ALMA.
Facilitator
-Name: Haruka Kusakabe
Comment: English