Home > ALMA Jセミナー | Solar and Space Plasma (SSP) Seminar | 国立天文台談話会 | 太陽系小天体セミナー | 科学研究部コロキウム > 2021.5.24-2021.5.30


May 25 Tue 10:00~11:30  太陽系小天体セミナー / Solar System Minor Body Seminar zoom

May 26 Wed 15:00~16:00  ALMA-J seminar           zoom

May 26 Wed 15:30~17:00  NAOJ Science Colloquium       zoom

May 28 Fri 13:30~15:00   Solar and Space Plasma Seminar    zoom         

May 28 Fri 16:00~17:00  談話会 / NAOJ Seminar      zoom           






Campus: Mitaka
Seminar: ALMA-J seminar
Regularly Scheduled/Sporadic: Every Wednesday
Date and Time: 2021 May. 26 15:00-16:00
Place: Zoom
Speaker:Kenichi Tadaki (NAOJ)
Title: ALMA reveals where stars are formed in massive galaxies at z=2
Abstract: At z~2, massive quiescent galaxies are extremely compact with a dense core while the majority of star-forming galaxies (SFGs) have a more extended stellar disk. High-resolution observations of dust continuum emission are powerful for understanding where stars are formed in galaxies since 99% of star formation is obscured by dust. We have made 1 kpc-resolution ALMA observations at 870 um for a mass-selected (logMstar>11) sample of 85 SFGs at z=1.9-2.6 in CANDELS/3DHST fields. Our sample is not biased towards submillimeter bright galaxies nor biased against optical morphology. We measured the effective radius of the rest-frame far-infrared emission for 62 massive SFGs. By combining the spatial distributions of the far-infrared (observed-frame 870 um) and optical (observed-frame 1.6 um) emission, it is possible to investigate how galaxies change the effective radius of the optical emission and the stellar mass. The effective radius of the far-infrared emission is smaller by a factor of 2.3 than the effective radius of the optical emission. As a result, the compact starburst puts most of the massive SFGs on the mass-size relation for quiescent galaxies at z~2 within 300 Myr if the current star formation activity and its spatial distribution are maintained. These results suggest an outside-in transformation scenario in which a dense core is formed at the center of a more extended disk, likely via dissipative in-disk inflows. Recent studies claim that even 1.6 um emission is significant affected by dust extinction, indicating that the stellar half-mass radius is smaller than the 1.6 um half-light radius. Synchronized observations at ALMA 870 um and James Webb Space Telescope 3-4 um will explicitly verify this issue.

Facilitator: Yuichi Matsuda, Yusuke Miyamoto


Seminar:NAOJ Science Colloquium
Regularly Scheduled/Sporadic:Every Wednesday
Date and time:2021 May 26, 15:30-17:00
Speaker:Yosuke Mizuno
Title:The Shadow of the Supermassive Black Hole in M87: EHT observations and theoretical modeling
Abstract:The Event Horizon Telescope has mapped the central compact radio source of the elliptical galaxy M87 at 1.3 mm with unprecedented angular resolution. These images show a prominent ring with a diameter of ~40 micro-arcsecond, consistent with the size and shape of the lensed photon orbit encircling the “shadow” of a supermassive black hole. In this talk, I would like to present recent progress of observation of EHT results of M87 and theoretical modeling and interpretation. We construct a large library of models based on general relativistic magnetohydrodynamic simulations and synthetic images produced by general relativistic ray tracing. We compare the observed visibilities with this library and confirm that the asymmetric ring is consistent with earlier predictions of strong gravitational lensing of synchrotron emission from a hot plasma orbiting near the black hole event horizon. I also briefly discuss about new results of polarimetric images of M87 and their theoretical interpretation.
-Name:Akimasa Kataoka


Campus: Mitaka
Seminar: Solar and Space Plasma Seminar
Regularly Scheduled/Sporadic: Sporadic
Date and time:28 May (Fri), 13:30-15:00
Place: zoom
Speaker:Munehito Shoda
Affiliation: NAOJ
Title:Modeling the corona and XUV emission of the Sun and Sun-like stars

The X-ray and extreme-ultra-violet (EUV) emission from the low-mass stars significantly affect the evolution of planetary atmosphere. It is, however, observationally difficult to constrain the stellar high-energy emission because of the interstellar extinction. In this work, we simulate the XUV (X-ray+EUV) emission from the Sun-like stars by extending the solar coronal heating model that self-consistently solves the surface-to-corona energy transport, turbulent energy dissipation, and coronal thermal response by conduction and radiation. The simulations are performed for a range of half loop length and magnetic filling factor at the stellar surface. When applied to the solar corona, our model is found to reproduce the observed solar XUV spectrum below the Lyman edge, which validates the capability of our model in predicting the XUV spectrum of other Sun-like stars. By assuming a power-law relation between the Rossby number and magnetic filling factor, the widely known relation between the Rossby number and X-ray luminosity is also reproduced. We also propose a coronal heating theory based on the conventional RTV scaling law and linear theory of the Alfven-wave transmission into the corona, by which we can analytically account for the numerically-obtained behaviors of the coronal properties with respect to the loop length and magnetic filling factor. This study demonstrates a refined picture of stellar coronal heating and provides the above observable relations that will be useful for estimating the luminosity of the hidden stellar EUV from X-ray observations.

-Name:Munehito Shoda


Seminar:NAOJ Seminar
Regularly Scheduled/Sporadic:Scheduled
Date and time:2021 May 28, 16:00~17:00
Speaker:村山 斉 / Hitoshi Murayama
Affiliation: カリフォルニア大学バークレー校 / 東京大学カブリ数物連携宇宙研究機構 
University of California, Berkeley / Kavli IPMU, the University of Tokyo

-Name:浜名 崇 / Hamana, Takashi

Home > ALMA Jセミナー | Solar and Space Plasma (SSP) Seminar | 国立天文台談話会 | 太陽系小天体セミナー | 科学研究部コロキウム > 2021.5.24-2021.5.30

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