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OUTAP Colloquium 2015

ホーム > コロキウム & セミナー > 宇宙進化コロキウムのご案内 > 2015年度の宇宙進化コロキウム
・・・・・2015年度の宇宙進化コロキウム・・・・・


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講演者 :Dr. Shinsuke Takasao (京都大学)
TITLE :Oscillations seen in solar flares: What can we learn from observations of oscillations?
Date : 2/22 (Mon)15:00~
LOCATION:F313

ABSTRACT:
Solar flares are an explosive phenomenon powered by magnetic reconnection, and are believed to be a prototype of various kinds of astrophysical explosions. Solar and many other astrophysical flares can be recognised as a sudden increase in a wide range of electromagnetic waves (from radio to gamma ray). It has been known that flares intrinsically show oscillations as pulsations in lightcurves and compressional waves propagating away from the flaring regions. Under the assumption that the oscillations are caused by magnetohydrodynamics (MHD) waves excited in flares, people have tried to derive physical parameters of solar and stellar flares which are difficult to directly measure. However, the mechanisms of the oscillations remain puzzling, and therefore the validity of the assumption is uncertain. To reveal the intrinsic oscillatory nature of solar flares, we carried out MHD simulations of solar flares. As a result, we discovered that simulated flares show characteristics similar to observations, and identified the mechanism which has never been expected. In this talk, I will begin with a brief introduction of the solar physics, and then will introduce our results. I will also discuss the importance of this finding in the astrophysical context.


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講演者 :Dr. Ken Mawatari (大阪産業大学)
TITLE :Discovery of a new type DLA: HI absorber along a galaxy sight-line
Date : 2/17 (Fri)15:00~
LOCATION:F313

ABSTRACT:
We have performed a series of spectroscopic observations of the LBGs and LAEs photometrically selected from the Subaru Scam imaging of the SSA22 field. Especially the VLT VIMOS observations in 2008 yields the high S/N spectra which enables us to investigate the intervening IGM HI absorptions. Using normal galaxies as background light sources to map the Lya absorption lines is a novel approach to study the intervening HI absorbers. In my talk, we focus on a z=3.3 DLA identified in a z=3.6 LBG sight-line. The DLA HI column density is as high as log(N_HI) = 21.7. By measuring the residual flux in the Lya trough we constrained the covering fraction of the DLA gas cloud over the background LBG, resulting a f_cov>0.7 or DLA area > 1 kpc^2. We searched for a galaxy hosting the DLA utilizing the deep multi-band images, resulting that there is no counterpart galaxy with SFR > a few solar mass. These properties are consistent with the previous measurements and theoretical predictions for QSO-DLAs. If the occurence rate of gal-DLAs is similar to that if QSO-DLAs the sample number of gal-DLAs will increase dramatically in the next decade, which open a new window in examining the DLA size and counterpart galaxies. I also plan to introduce our new survey, HIT, to investigate the HI absorption systems.


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講演者 :Dr. Kent Yagi (プリンストン大学)
TITLE :Probing Fundamental Physics with Universal Relations for Neutron Stars
Date : 1/22 (Fri)13:30~
LOCATION:F217

ABSTRACT:
Neutron stars offer us an excellent testbed to probe fundamental physics, such as nuclear physics and strong-field gravity. Unlike the well-studied mass-radius relation for neutron stars that depends strongly on their internal structure, I first report unexpected universal relations that we found among the moment of inertia, tidal Love number and quadrupole moment ("I-Love-Q" relations) that are insensitive to the internal structure. Such universal relations help us break the degeneracy among neutron star parameters when probing fundamental physics with radio, X-ray or gravitational wave observations. In the second part of my talk, I report another universal relations among tidal parameters in gravitational waves from neutron star binaries. Such relations have applications not only to gravitational wave astrophysics, but also to nuclear physics as they improve the measurement accuracy of tidal parameters. Moreover, the relations improve our ability to test extreme gravity and perform cosmology with gravitational waves emitted from neutron star binaries.


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講演者 :Genoveva Micheva 氏 (Subaru Telescope, NAOJ)/SPEAKER :Dr. Micheva (Subaru Telescope, NAOJ)
TITLE :High-z sources of Lyman Continuum from the SSA22 field
DATE :11/11(wed)15:00~
LOCATION:F313

ABSTRACT:
The escape fraction of Lyman continuum (LyC) is the fraction of hydrogen ionizing radiation that escapes from a galaxy into the intergalactic medium (IGM) and contributes either to reionizing the Universe at redshifts z>6 or to keeping it ionized at lower redshifts. In this talk we will present the largest to date sample of LyC emitting galaxies at any redshift, with 18 Lyman Alpha Emitters (LAEs) and 7 Lyman Break Galaxies (LBGs), obtained from the SSA22 field with Subaru/Suprime-Cam. A spatial offset is often detected between the rest-frame non-ionizing ultraviolet (UV) detection and the LyC-emitting substructure or between the LyA emission and LyC. We show that statistically it is highly unlikely that all LyC candidates are foreground contaminants. From comparison to stellar evolutionary models (SEDs) both LAEs and LBGs hosting the LyC escape seem to require extremely metal-poor or even metal-free young (zero-age) populations. We further show that "standard" SED models cannot fully explain the observed LyC LAEs colors, and require exotic models instead, with a top-heavy initial mass function with an average stellar mass of ~100 M_sun and the "Lyman limit bump" model which postulates an escape of nebular recombination LyC. We find some evidence for a positive LyC/LyA correlation, suggesting that both LyC and LyA escape via a similar mechanism. The LyC emission seems to be bimodal - stacking non-detections reveals no significant LyC signal strength. From LyC detections we obtained estimates of LyC escape fraction of ~20% for LyC LBGs and ~30% for LyC LAEs, assuming an SMC dust law. From non-detections we obtain 3 sigma median upper limits on the flux density ratios as f(LyC)/f(UV)<0.08 from 143 non-LyC LAEs, and f(LyC)/f(UV)<0.02 from 133 non-LyC LBGs. We will also introduce a new Subaru intensive program on the "Cosmic HydrOgen Reionization Unveiled with Subaru" (CHORUS). The project will target the 3 central issues of Cosmic reionization: ionization sources, history, and topology.


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講演者 :John D. Silverman 氏 (Kavli Institute for the Physics and Mathematics of the Universe: Kavli IPMU)/SPEAKER :Prof. Silverman (KIPMU)
TITLE :Environmental influences on growing supermassive black holes
DATE :10/14(wed)15:00~
LOCATION:F313

ABSTRACT:
TBD


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講演者 :平下 博之 氏 (Academia Sinica, Institute of Astronomy and Astrophysics: ASIAA)/SPEAKER :Prof. Hirashita (ASIAA)
TITLE :Modeling the dust evolution in galaxies
DATE :9/16(wed)15:00~
LOCATION:F313

ABSTRACT:
The evolution of dust in galaxies is characterized by two aspects; dust abundance and grain size distribution, both of which are important in determining the radiative properties of galaxies through dust extinction and emission. Recently we have been developing a theoretical framework that treats these two aspects consistently. In this presentation, I introduce our dust evolution models. I will also talk about some predictions about the evolution of extinction curve, which are compared with observations. Finally I also mention our plan of implementing our models in hydrodynamic galaxy evolution simulations.


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講演者 :門田 健司 氏 (enter for Theoretical Physics of the Universe (CTPU), Institute for Basic Science (IBS))/SPEAKER :Prof. Kadota (IBS)
TITLE :Constraining the dark matter from 21cm signals
DATE :7/29(wed)15:00~
LOCATION:F313

ABSTRACT:
The future prospects for the constraints on the particle dark matter from the 21cm signals will be presented. The effects of the dark matter interactions with the baryons on the 21 cm observables will be discussed, along with its comparison with the complementary bounds from the direct dark matter search experiments.


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講演者 :細川 隆史 氏 (東京大学)/SPEAKER :Prof. Hosokawa (Tokyo University)
TITLE :Formation of Massive Primordial Stars
DATE :4/22(wed)15:00~
LOCATION:F313

ABSTRACT:
The mass accretion process onto growing primordial stars is very dynamic in general, sometimes showing very time-dependent accretion histories. In this talk, I present our recent 3D radiation-hydrodynamic simulations following such dynamic accretion process under the stellar UV feedback. Our calculations, which also solve the stellar evolution simultaneously, show that massive primordial stars with M > 250 Msun can form circumventing the UV feedback. In such cases, we see a 3D effect which helps forming massive stars; the accretion burst with > 0.01 Msun/yr makes the star largely inflate, so that an HII region forming around the star suddenly disappears. Even more rapid and variable mass accretion should be expected in some extreme cases for providing massive seeds of SMBHs, e.g., in so-called direct-collapse case. I also discuss potential impacts of the burst accretion for forming supermassive stars in the early universe.

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コロキウムの予定表はこちら/ Schedule of colloquium