Home > ALMA Jセミナー | Solar and Space Plasma (SSP) Seminar | 太陽系小天体セミナー | 科学研究部コロキウム > 2021.6.7-2021.6.13


Jun 8 Tue 10:00~11:30  Solar System Minor Body Seminar  zoom

Jun 9 Wed 15:00~16:00  ALMA-J seminar          zoom

Jun 9 Wed  15:30~17:00  NAOJ Science Colloquium       zoom

Jun 11 Wed 13:30~15:00 Solar and Space Plasma Seminar    zoom       






Campus: Mitaka
Seminar: ALMA-J seminar
Date and Time: 2021 June 9, 15:00-16:00
Place: Zoom
Speaker:Takuji Yamashita (NAOJ)
Title:Radio galaxies in the early universe found in Subaru HSC-SSP
I present the recent results of our on-going high-z radio galaxy survey project which is called “Wide and Deep Exploration of Radio Galaxies (RGs) with Subaru HSC (WERGS)”. High-z RGs (HzRGs) represent a key population for understanding the evolution and formation of massive galaxies in the early universe, because radio-jets launch from RGs could regulate star formation in galaxies. However, the number of known HzRGs are very limited due to their rareness and faintness. We utilize the wide and deep-field Subaru Hyper Suprime-Cam (HSC) survey catalog and archival deep radio data to construct a new and large HzRG sample. We found 23 HzRGs at z > 4 in the Subaru HSC survey region. I show our recent results from the sample. First, I show a spectroscopically confirmation of a z=4.7 HzRG and its host galaxy property. Second, statistical properties of our HzRGs using analyses of archival radio, optical-IR data, and our JVLA folllow-up observation. Finally, I talk about the planned follow-up observation with ALMA and other facilities.

Facilitator: Yuichi Matsuda, Yusuke Miyamoto


Seminar:NAOJ Science Colloquium
Regularly Scheduled/Sporadic:Every Wednesday
Date and time:2021 June 9, 15:30-17:00
Speaker:Sebastian Marino
Affiliation:Jesus College Cambridge
Title:Studying ExoKuiper belts through ALMA observations
Abstract:Planetary systems are not only composed of planets but also of minor bodies similar to asteroids and comets, which we typically find in belts analogous to the Asteroid and Kuiper belt in the Solar System. Although we cannot detect these bodies individually, mutual collisions between these km-sized planetesimals produce high dust levels that are readily detectable in exoKuiper belts around 30% of nearby stars. These planetesimals form as a byproduct of planet formation and their distribution is shaped by the presence of planets in a similar way as the Asteroid and the Kuiper belts were shaped by Jupiter and Neptune. Therefore, these belts provide unique and complementary constraints on the formation, architecture, and dynamics of planetary systems. In this Colloquium, I will show how I have used ALMA and numerical simulations to constrain the radial structure and volatile composition of Kuiper belt analogues (exoKuiper belts), and their implications for planetesimal formation, the presence of Neptune analogues, and volatile delivery to the inner regions of planetary systems.

-Name:Akimasa Kataoka


Campus: Mitaka
Seminar: Solar and Space Plasma Seminar
Regularly Scheduled/Sporadic: Scheduled
Date and time:11 June (Fri), 13:30-15:00
Place: zoom
Speaker:Takashi Sakurai
Affiliation: NAOJ
Title:Probability distribution functions of sunspot area and flare energy revisited

Studies in the past show that the size of the magnetic field structures
(active region flux, sunspot size, etc.) roughly follows a power law.
But power laws extend to infinity, and whatever the probability is
small, you have probability of having infinitely large magnetic
concentration, which may contradict with the finite size of the Sun.
We reconsidered the distribution function of the magnetic flux of
sunspots systematically. We assumed a power-law distribution (with one
parameter, the power exponent), and several two-parameter distributions.
The parameter values are determined by the maximum likelihood estimator.
Whether a particular model is better than the other is judged by
comparing AIC. Whether a particular model is statistically rejected or
not is judged by the Kolmogorov-Smirnov criteria.
Using sunspot area data from 1874 to 2020 (147 years), we found that
power laws are rejected, and two-parameter distribution functions with a
power law tapered by an exponential decay give better fits. The maximum
sunspot size is expected to be around 15000 MSH (the largest recorded
sunspot region is 6132 MSH).
A similar analysis is applied to the GOES X-ray emission. Aside from
possible detector saturation for energetic flares, the same conclusion
holds and the power-law-like distributions tapered by an exponential
decay give better fits. The maximum possible solar flare would be around
X300. A similar analysis is under way for stellar flares, and we may
report preliminary results.

-Name:Munehito Shoda

Home > ALMA Jセミナー | Solar and Space Plasma (SSP) Seminar | 太陽系小天体セミナー | 科学研究部コロキウム > 2021.6.7-2021.6.13

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