[日時] 毎週月曜日15時から / [Date] Monday 15:00-
|1626||2020/10/08 (Thu 9:00-)||Online||Chengchao Yuan (Penn State)||Galaxy and SMBH mergers in the era of multi-messenger astrophysics|
|1627||2020/10/12 (Mon)||Online||Yutaka Hirai (RIKEN)||Enrichment of Heavy Elements in Dwarf Galaxies and the Milky Way|
|1628||2020/10/19 (Mon)||Aoba Science Hall||Mariko Kubo (Ehime U.)||Detailed case and statistical studies of protoclusters|
|1629||2020/11/2 (Mon)||Aoba Science Hall||Kohei Hayashi (Tohoku U.)||The Galactic dwarf galaxy as a constraint on the nature of dark matter|
|2020/11/30||第1講義室 (理学合同A棟203)||定成 健児エリック|
|2020/12/09 (Wed 16:00-)||online||Kenji Furuya (NAOJ)|
|2020/12/14||多目的室||小野 遥香、青山 晧平|
|2020/12/21||第1講義室 (理学合同A棟203)||雨宮 竜登、飯塚 悠太|
2020/10/08 (Thu) 9:00-
Chengchao Yuan (Penn State)
Galaxy and SMBH mergers in the era of multi-messenger astrophysics
Recently, the coincident detection of gravitational waves (GWs) and electromagnetic (EM) counterpart from binary neutron star mergers heralds a new era of multi-messenger astronomy. Beginning in 2012-2013 by the discovery of the cosmic high-energy neutrino background, neutrino astrophysics also plays an important and indispensable part in the future multi-messenger analyses. In this talk, I’ll focus on the neutrino and EM emissions from two important candidates, galaxy mergers and super-massive black hole mergers, for the next generation neutrino and GW detectors, e.g. IceCube-Gen2 and LISA. I’ll show that our results together with future detections can be used to elucidate the evolution and the physical mechanism of these sources in greater details.
2020/10/12 (Mon) 15:00-
Yutaka Hirai (RIKEN)
Enrichment of Heavy Elements in Dwarf Galaxies and the Milky Way
Abundances of heavy elements in metal-poor stars help us understand their astrophysical sites and evolutionary histories of galaxies. High-dispersion spectroscopic observations have identified that abundances of neutron-capture elements such as Sr, Ba, and Eu show star-to-star scatters in extremely metal-poor stars in the Milky Way while there is an increasing trend toward lower metallicity in the abundance of Zn. However, their astrophysical sites and the enrichment in galaxies are not well understood. Here I will show the enrichment of heavy elements of dwarf galaxies and the Milky Way using N-body/smoothed particle hydrodynamics simulations. The results suggest that binary neutron star mergers can contribute to the enrichment of Sr, Ba, and Eu for [Fe/H] < −2. Likewise, this study finds that ejecta from supernovae by low-mass progenitors can form stars with high [Zn/Fe] and [Sr/Ba] ratios. In this talk, I will also discuss relationships among abundances of elements, kinematics of stars, and the Milky Way formation.
2020/10/19 (Mon) 15:00-
Mariko Kubo (Ehime U.)
Detailed case and statistical studies of protoclusters
Protoclusters are interesting laboratories to study how galaxies have evolved interacting with their environments and acquired the environmental dependence today, and test the cosmological structure formation scenario. In this talk, I will present our latest studies of one of the most well studied protocluster, the SSA22 protocluster at z=3.09, and statistical studies of protoclusters with Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP).
The SSA22 protocluster is one of the most significant protocluster which is at the density peak of a large scale structure extending to 60~100 Mpc. Based on our own deep multi-wavelength observations, including the GTO MOIRCS deep and wide imaging observations, we found that passively evolving, modern cluster galaxies have already appeared but still quite active starburst is on-going in this protocluster. Such detailed studies of protoclusters give us very important lessons: the properties of protoclusters in optical is just a tip of a large iceberg even at z>3, and large statistical studies are needed since the properties of protoclusters range widely even at similar redshift. Now the first systematic survey of protoclusters was performed with HSC-SSP in Toshikawa et al. (2018). They found 179 candidate protoclusters at z~4 as the overdensities of g-dropout galaxies selected from the public data release 1 of WIDE layer. To study the star formation obscured by dust, we need to observe the re-emission from dust at infrared. We performed a stacking analysis of the infrared archival images from e.g., Planck survey at the positions of HSC-SSP protoclusters, and successfully show the average total mid to far IR flux of a protocluster at z~4, for the first time. The total IR luminosity of a protocluster is on average three times brighter than that expected from the optically selected galaxies. In addition, their dust temperature is higher than that of a typical star forming galaxy; it indicates the overdensities of young hot starburst galaxies or obscured AGNs in protoclusters. I will also discuss future prospects for such multi-wavelength (statistical) studies of protoclusters.
Kohei Hayashi (Tohoku U.)
The Galactic dwarf galaxy as a constraint on the nature of dark matter
Dark matter is now known to be the vital ingredient for the growth of structure in the Universe, while its nature remains a mystery. The dwarf galaxies are excellent laboratories to study the nature of dark matter as they are largely dark-matter dominated systems. In particular, revealing their dark matter distributions is of importance in testing dark matter models. This is because different dark matter models predict different dark matter density profiles. In this work, we estimate the dark matter distributions in the eight luminous dwarf satellites through our dynamical analysis of their stellar-kinematic data. Then we find the diversity of the inner slopes in their dark matter halos. Interestingly, this diversity can be explained if we consider the impact of baryonic feedback on the central dark matter densities, which depends largely on the ratio of stellar-to-halo mass as predicted by recent Lambda cold dark matter and hydrodynamical simulations. Thus, to set constraint on the nature of dark matter, it is necessary to look at much fainter dwarfs, namely ultra-faint dwarfs, which are believed to have held original dark matter density profiles.
In this talk, I will present our effort to characterize the dark matter distributions of dwarf galaxies with current spectrographs. Then, I will discuss the feasibility and future prospects for this dark matter study with Subaru-PFS survey.