談話会
Colloquium

早川 尚志 (大阪大学)
キャリントン・イベントと極端宇宙天気現象：同時代観測に基づく復元
太陽から放出されたコロナ質量放出が地球の磁気圏に衝突すると、大規模な磁気擾乱とオーロラ活動を引き起こすことがある。このような一連の地球近傍の宇宙環境の変動を宇宙天気現象と称するが、その中でも特に極端なものは電信インフラに依存する現代社会にとって大きな脅威となることが知られている。宇宙天気現象中、観測史上最大とされるものは1859年の9月に生じたキャリントン・イベントとされるが、その規模推定には大きなばらつきがあり、1950年代にデータベースが整備されて以降の既知の宇宙天気現象に対する当該イベントの位置付けは必ずしも固定されたものではなかった。そこで本研究では、未検討の同時代黒点スケッチと東半球のオーロラデータを検討してキャリントン・イベントの詳細な展開を明らかにし、オーロラ・オーバルの広がりを他の極端宇宙天気現象と比較することで、キャリントン・イベントの規模と独自性について検討する。同時代観測との比較から、キャリントン・イベントは確かに最大級の宇宙天気現象であったことが実証されるが、1872年や1921年にも同様の規模の宇宙天気現象が同定されたことから、類例のない巨大現象とすることはできないことが明らかになった。

Jose Manuel Perez Martinez (Tohoku U.)
The evolution of kinematic scaling relations in clusters at 0.5 < z < 1.5
The evolution of galaxies across cosmic time requires several physical processes acting together to reproduce the galaxy populations we see in the local Universe today. In clusters, these transformations are boosted by the influence of environmental effects acting on both the stellar structure and the gas reservoir. For regular rotating spiral galaxies, the maximum circular velocity, the effective radius, and the stellar-mass allow us to examine the evolution of several kinematical scaling relations such as the Tully-Fisher relation, the velocity-size relation and the angular momentum-stellar mass relation. At z<1, we find no significant statistical differences in the evolution of these scaling relations between the cluster and field environments. However, at z>1, cluster galaxies become exceedingly luminous (in B-band) in the TFR, display smaller sizes than expected in the VSR, and show a faster redshift evolutionary trend in the angular momentum-stellar-mass relation with respect to their field counterparts. In this talk, I will discuss the probable causes and implications of these findings in the context of galaxy evolution in clusters across cosmic time.

G. C. Anupama (Indian Institute of Astrophysics)
India's venture in the future large telescope project - the Thirty Meter Telescope
The Thirty Meter Telescope (TMT) will be the world’s most advanced and capable ground-based optical, near-infrared, and mid-infrared observatory. It will integrate the latest innovations in precisions control, segmented mirror design, and adaptive optics. At the heart of the telescope is the segmented mirror, made up of 492 individual segments. Precisely aligned, these segments will work as a single reflective surface of 30m diameter. The Thirty Meter Telescope project is an international partnership between Caltech and the Universities of California (U.S.A), Canada, Japan, China and India. All partners are contributing to the build of several subsystems. In this talk I will provide a brief on India's contributions to the project. I will also discuss in brief India's proposal for a 10m class telescope in the country.

Shigeo Kimura (Tohoku U.)
High-energy Neutrino and Gamma-ray Emissions from Accretion Flows in Active Galactic Nuclei
IceCube Collaboration reported the discovery of the astrophysical neutrinos in 2013, but the source of the neutrinos is still veiled in mystery. In this talk, I will discuss neutrino and gamma-ray emissions from accretion flows in active galactic nuclei (AGNs). We present two models: luminous AGN and low-luminosity AGN (LLAGN) models. In the luminous AGN model, we consider proton acceleration in a hot corona above a cold disk. The accelerated protons interact with target photons and produce neutrinos and gamma rays. Since the gamma rays are attenuated by the soft photons, the luminous AGN model can reproduce IceCube data without overshooting the gamma-ray background measured by Fermi. In the LLAGN model, protons are accelerated in a radiatively inefficient accretion flow (RIAF) and emit neutrinos and gamma rays mainly interactions with thermal protons. The LLAGN model can explain the IceCube data and the MeV gamma-ray background simultaneously. Future multi-messenger observations of high-energy neutrinos and MeV gamma rays will provide stringent tests of our model.

Rainer Schodel (Instituto de Astrofisica de Andalucia)
Near-infrared observations of the centre of the Milky Way
The Galactic Centre (GC) is located at only 8 kpc from Earth. It is a unique target and of fundamental importance for astrophysics because it is the only galactic nucleus where we can resolve stars on milli-parsec scales. The GC is also the most extreme environment and most important massive star forming region in the Milky Way. In this talk I will review our current knowledge, discuss observational challenges and methodologies, and address central objectives of GC research.