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Abstract: One of the big unsolved questions in galaxy evolution is how the star-formation activity in galaxies stop and the transformation of morphologies, and how this process and governing mechanisms evolve in cosmic time.
This talk will focus on z=1 and later, the period that the cosmic star-formation rate density drops rapidly. I will introduce our recent large spectroscopic campaign, the LEGA-C survey, which obtains 3000 ultra-deep optical spectra of galaxies z~1 using 100 nights of the Very Large Telescope. The high-S/N spectra probe the ages and the assembly histories of galaxies through stellar continua. Combing the structural parameters from HST images, I will demonstrate that there is no one simple mechanism that can explain the complex correlation between the formation histories and structures of galaxies. The majority of galaxies likely went through a gentle process that shuts down star-formation slowly without altering the structure, while some galaxies are experiencing rapid change in both star-formation rate and structural at the same time.
I will further show follow-up studies on post-starburst galaxies, those undergo the rapid decline of star-formation rates, to investigate the driving mechanisms. Various pieces of evidence suggest that post-starburst galaxies had a centrally-concentrated starburst event before the star-formation activity halts.
Note: we will provide a zoom link, so you can join the seminar remotely.
Abstract: Solar flares are explosive phenomena on the solar surface. They often produce high XUV radiations, high energy particles, and mass ejections which have potential risks to damage human technologies. On other stars, such as M dwarfs and young stars, larger ‘superflares’ (more than ten times larger than the most energetic solar flares) are known to frequently occur, severely affecting the exoplanet habitability. Recently, there is an increasing interest in the question “How do the stellar magnetic activities on central stars affect the planetary environment?”, and therefore the properties of stellar superflares become more and more important. Optical spectroscopic observations have a potential to reveal the properties of superflares, but the detections of ssuperflares have been very rare due to its low occurrence frequency. We have conducted optical spectroscopic observations of stellar superflares on M-/G-dwarfs with the 3.8-m Seimei telescope since 2019. We have succeeded in detecting optical spectra of the rare stellar superflares with very high time-cadence and high quality. We found a very dynamic change in optical spectra during a superflare as evidence of strong injections of high-energy particles to the stellar atmosphere (Namekata et al. 2020b). Moreover, we detected the first, conclusive evidence of stellar mass ejection, which revealed the mechanism of mass ejections and would enable us to estimate its direct impact on exoplanets (Namekata et al. submitted). In this talk, I will talk about the recent results by the Seimei telescope.
東京大学・天文学教育研究センターでは2003年4月から, 院生コロキウムに引き続き, 談話会を開いています. 第一線で活躍されている研究者の方々を講師にお招きし, 最先端の研究成果をお話しいただきます. 講師の方には, 大学院生の参加者のことも考慮し, レビュー的な側面も含めた上で, ご自身の研究紹介をお願いしています.
| 13:30-14:30 | 院生コロキウム | 講義室 |
| 15:30-16:30 | 談話会 | 講義室 |
| 16:30- | お茶の時間 | 講義室横のお茶部屋~講師の方を交えて~ |
ML: semiadm _at_ ioa.s.u-tokyo.ac.jp
please replace _at_ to @
| # | Date | Speaker | Title | Chair |
| 359 | 2020/10/08(Thu) 15:30 - 16:30 | 吳柏鋒 Wu, Po-Feng (EACOA Fellow/NAOJ) | The blind men and the elephant: Multiple evolutionary paths from star-forming galaxies to quiescence | TT |
| 360 | 2020/10/15(Thu) 15:30 - 16:30 | 行方宏介 Namekata, Kosuke (京都大学) | Stellar superflares on late-type stars - recent results by 3.8-m Seimei telescope | TM |
詳細はこちら: 平成31(2019)年度談話会
| # | Date | Speaker | Title | Chair |
| 345 | 2019/04/01(Mon) 15:30 - 16:30 | J. Xavier Prochaska (UCO/Lick Observatory) | The Wolfe Disk: ALMA Discoveries of Distant, HI-selected Galaxies | KK |
| 346 | 2019/06/27(Thu) 15:30 - 16:30 | Yuu NIINO (IoA/Univ. of Tokyo) | The origin of short and intense explosions in the universe | KK |
| 347 | 2019/07/02(Tue) 16:00 - 17:00 | Wakiko ISHIBASHI (University of Zurich) | How AGN radiative feedback may shape black hole-galaxy co-evolution | KK |
| 348 | 2019/07/04(Thu) 15:30 - 16:30 | Hidenobu YAJIMA (Univ. of Tsukuba) | Cosmological simulations of galaxy formation at the epoch of reionization | KK |
| 349 | 2019/07/11(Thu) 15:30 - 16:30 | Fumihiko USUI (Kobe University) | 近赤外線分光観測による小惑星の含水鉱物探査 | RO |
| 350 | 2019/08/26(Mon.) 15:30 - 16:30 | Glenn Orton (NASA/JPL) | The Exploration of Jupiter by the Juno Mission | RO |
| 351 | 2019/10/2(Wed) 13:15 - 14:15 | 吉田健二 Kenji Yoshida (芝浦工業大学) | Correlations between Optical/Infrared and Gamma-ray Variability in Bright Well-Monitored Blazars 2008-2017 | YN |
| 352 | 2019/10/24(Thu) 15:30 - 16:30 | 橋本哲也 Tetsuya Hashimoto (台湾国立清華大学) | Recent three discoveries from NTHU cosmology group | YN |
| 353 | 2019/10/28(Mon) 13:00 - 14:-0 | Kevin Fogarty (Caltech) | Cooling and Condensation in Cool-Core Galaxy Clusters: the Case of MACS 1931.8-2635 | KK |
| 354 | 2019/10/31(Thu) 15:30 - 16:30 | 徳田一起 Kazuki Tokuda (Osaka Prefecture University) | ALMAによる大小マゼラン雲とM33の巨大分子雲観測 ALMA observations of GMCs in the Large/Small Magellanic Clouds and M33 | KK |
| 355 | 2019/11/07(Thu) 15:30 - 16:30 | 高倉理 Satoru Takakura (IPMU/U.Tokyo) | A measurement of the degree-scale CMB polarization with POLARBEAR | KK |
| 356 | 2019/11/14(Thu) 14:30 - 15:30 | Ewine van Dishoeck (Leiden Univ.) | Molecules from clouds to disks and planets | KK |
| 357 | 2019/12/05(Thu) 15:30 - 16:30 | 鮫島寛明 Hiroaki Sameshima (IoA/U.Tokyo) | Spectroscopic studies on quasars and stars | YN |
| 358 | 2019/12/12(Thu) 15:30 - 16:30 | 坂野正明 Masaaki Sakano (Wise Babel) | 英語の『数』を考える — 冠詞、単数複数、非可算 | KK |
