GALACTIC WINDS: Physics, Phenomenology, and Implications
Timothy Heckman (Johns Hopkins University)
I will review galactic winds driven by populations of massive stars. I will describe the basic physics that drives winds and dictates their impact on the interstellar and circum-galactic medium. I will describe observations of the multi-phase outflow in the proto-typical starburst galaxy M 82. I will then discuss the systematic dependence of wind properties on such key parameters as the star-formation-rate, galaxy size, and mass (circular velocity), and show that there explain the strong rise in the incidence rate of winds with redshift. I will also compare these empirical scaling relations with sub-grid recipes commonly adopted in models and simulations. Finally, I will describe observations that demonstrate the impact of winds on the chemical evolution of galaxies and on the properties of the circum-galactic medium.
Machine Learning for Classification of Astronomical Data
Tilman Hartwig (物理学専攻 / Department of Physics)
I will give an overview of machine learning techniques and present decision trees as very efficient machine learning tool to classify astronomical data. A labelled training sample is split according to available features by requiring that each split minimises the information entropy of the assigned classes. This elegant mathematical formulation allows us to construct decision trees with supervised learning, which can then be applied to classify new observations.
Eventually, I will present recent results of my own research: by classifying the chemical abundance patterns of metal-poor stars in the Milky Way, we can derive the multiplicity of the first generation of stars in the Universe. Furthermore, this approach provides the feature importance to identify crucial chemical elements to classify metal-poor stars, which can be used to optimise future spectroscopic surveys of Milky Way stars.
Direct Detection of Nano-Herz Gravitational Waves with Pulsar Timing Array
高橋 慶太郎 (熊本大学) / Keitaro Takahashi (Kumamoto University)
Pulsar timing array is a unique way to detect gravitational waves of nano-Hz frequencies and will greatly contribute to the multi-wavelength gravitational-wave astronomy. The major sources of nano-Hz are super-massive black hole binaries and cosmic strings, and we can probe structure formation of the universe in a different way from the other methods. In this talk, I will review the basic idea of pulsar timing array and the current status, and then give prospects for a future project, SKA (Square Kilometre Array).
hongo-astrotalks (at-sign) astron.s.u-tokyo.ac.jp