[Title and Abstract]
- School Year: 4th year (NAOJ)
- Name: Moka Nishigaki (西垣 萌香)
- Title: The fundamental metallicity relation of JWST galaxies in the early universe
- Abstract:
Galaxies evolve through various processes, including star formation,
gas inflow from the intergalactic medium, and gas outflows driven by
stellar and AGN feedback. A key relationship for understanding these
evolutionary processes is the fundamental metallicity relation (FMR),
which links gas-phase metallicity, stellar mass, and star formation
rate. In this study, we analyze the averaged galaxy spectra obtained
from the James Webb Space Telescope (JWST). Our results indicate that
galaxies at redshifts z>6 exhibit lower metallicities than predicted
by the FMR established at z∼0. This suggests that metal enrichment
processes maybe different in the early universe.
- School Year: 4th year (KEK)
- Name: Yuma Furuta (古田 悠真)
- Title: Lyth Bound and Swampland Distance Conjecture
- Abstract:
Inflation is the epoch with exponential expansion of spacetime of our
universe. Lyth bound is known that it gives a lower bound of
inflation model with respect to the tensor to scalar ratio. I will
discuss the relationship of Lyth bound and Swampland distance
conjecture.
- School Year: 3rd year (NAOJ)
- Name: Itsuki Ogami (小上 樹)
- Title: The Nature of the Stellar Halo in the Andromeda Galaxy Explored with the Subaru/HSC
- Abstract:
In the hierarchical structure formation scenario predicted by the
ΛCDM model, large spiral galaxies such as the Milky Way are thought
to have been formed by the accretion and merger of smaller stellar
systems. As these accreted systems are deposited into the stellar
halo, the halo serves as a crucial observational region for unraveling
a galaxy’s accretion history. The stellar halo of the Andromeda
galaxy (M31) presents an ideal target for studying galaxy formation,
owing to its proximity and the ability to observe its entire halo
structure. However, because M31 is located at low Galactic latitude,
its halo stars (red giant branch stars; RGB stars) are heavily
contaminated by foreground stars (dwarf stars), making it challenging
to resolve the detailed halo structure accurately. To overcome this
problem, we investigate the structures of M31’s stellar halo using
data obtained with Subaru/Hyper Suprime-Cam/NB515. The NB515 filter
enables the separation of M31 RGB stars from foreground Galactic dwarf
stars with an accuracy of approximately 90％. By analyzing the radial
profile of the extracted RGB stars, we examine the properties of
M31’s outer halo out to a projected radius of 300 kpc. Our key
findings are as follows, with further details to be presented in this
talk: 1. A single power-law profile well describes the stellar halo of
M31 out to 100 kpc, and no clear transition between an inner and outer
halo, as observed in the Milky Way, is found. 2. The halo structure
up to 150 kpc is well approximated by a power-law with an index of ∼
−2, which is shallower than the typical power-law index of ∼ −3
estimated for many nearby spiral galaxies. 3. A break in the radial
profile is identified at ∼150 kpc, a location comparable to that
observed in the Milky Way.
- School Year: 2nd year (KEK)
- Name: Mikage Kobayashi (小林 海景)
- Title: Gravitational wave background from supermassive black hole binaries and active galactic nuclei observed by JWST
- Abstract:
Recently, several collaborations of the James Webb Space Telescope
(JWST) have reported the existence of more Active Galactic Nuclei
(AGNs) than expected by the Lambda CDM model. A supermassive black
hole (SMBH) inside such an AGN can contribute to the gravitational
wave background (GWB) at O(0.001) - O(0.01) Hz through the mergers of
the binary SMBHs. In this study, we calculated the GWB signals taking
into account the mass function of these AGNs in the high redshift
bands. We found that the spectrum of the GWB becomes much larger than
predicted in the sensitivity region such as LISA, DECIGO or BBO.
School Year: 4th year (NAOJ)
Name: Toya Suzuki (鈴木 卓哉)
Title: Dark Matter Decay Around The Primordial Black Hole
Abstract:
Unlike traditional black holes, it has been suggested that primordial
black holes form due to curvature fluctuations in the early universe.
This primordial black hole is one of the candidates for dark matter.
It has also been suggested that halo composed of dark matter can also
form around a primordial black hole. In this presentation, we
calculated the flux of photons produced by the decay of dark matter in
order to find evidence for the existence of dark matter.
- School Year: 4th year (KEK)
- Name: Sakiko Nishimura (西森 早紀子)
- Title: Study toward a high-precision estimation of neutrino production in a long baseline neutrino oscillation experiment searching for CP violation in the leptonic sector
- Abstract:
T2K (Tokai-to-Kamioka) is a long-baseline neutrino oscillation
experiment in Japan, aiming to investigate CP violation in the
leptonic sector through neutrino oscillations. The latest results
exclude CP conservation at the 90% confidence level. Enhancing the
precision of oscillation analyses requires reducing beam-related
systematic uncertainties, one of which originates from neutrino flux
estimation in T2K’s beam Monte Carlo simulations. These flux
uncertainties play a crucial role in determining neutrino oscillation
parameters. This talk presents the latest studies addressing these
uncertainties.
- School Year: 5th year (NAOJ)
- Name: Ko Hosokawa (細川 晃)
- Title: Experimental Study of Molecular Line Broadening for Investigating the Atmospheres of Exoplanets and Brown Dwarfs
- Abstract:
Thousands of extrasolar planets and brown dwarfs (objects with masses between stars and planets) have been discovered so far, analyzing the atmospheric high-resolution spectra is becoming the main method for their study. In their atmosphere, Methane (CH4) is considered one of the key molecules that has a significant absorption in the spectra, but current spectral databases lack accurate absorption line shape data on CH4 in their environment. We experimentally obtained the line shape under their environment, mostly rich in hydrogen and helium. By constructing the experimental system that measures the transmission spectra of the simulated gas mixture up to T = 1000 K, we obtained line-broadening parameters for 22 spectral lines. Our findings show up to 5% object flux differences in brown dwarf compared to existing databases. This work improves the accuracy of atmospheric studies, benefiting upcoming high-resolution observations with next-generation telescopes.
- School Year: 4th year (KEK)
- Name: Junichi Yoshida (吉田 順一)
- Title: Advancement of Dose Calculation in Tadiation Therapy
- Abstract:
In radiation therapy, multiple dose calculations must be performed in
advance to develop an optimal treatment plan. Currently, clinical
practice relies on approximation methods for these calculations, which
can introduce errors in accuracy. To address this limitation, we
propose the development of a high-precision, high-performance dose
calculation application by accelerating Monte Carlo-based
simulations. Additionally, we aim to leverage highly accurate data to
automate complex tasks in radiation therapy planning using AI, thereby
improving efficiency and treatment quality.
- School Year: 3rd year (NAOJ)
- Name: Kyosuke Sato (佐藤 恭輔)
- Title: The star formation and chemical evolution history of Ursa Minor dwarf galaxy
- Abstract:
In the current ΛCDM cosmological model, dwarf galaxies are regarded as the smallest building blocks of hierarchical structure formation, spanning from small to large scales. The proximity of Galactic dwarf galaxies allows us to observe them as systems of resolved stars, allowing us to study galaxy formation and evolution processes in incredible detail.
We derived the star formation history (SFH) and metallicity distribution (MD) of Ursa Minor dwarf spheroidal galaxy (UMi dSph) simultaneously from the Subaru/HSC wide-field data. We also show the age-metal relations (AMR) based on the SFH and MD, and it is useful for understanding past events in stellar systems. The metal-poor population ([Fe/H]~ −2.5) and metal-rich population ([Fe/H]~ −2.2) of UMi dSph were distinguished by the AMR. Meanwhile, the star formation peak of the metal-rich population is 0.5Gyr younger than the metal-poor population. The star formation of different metallicities at comparable ages suggests a dwarf-dwarf merger event in the past.
- School Year: 4th year (KEK)
- Name: TREUER LUKAS DANIEL (ルーカス ダニエル トロイヤ)
- Title: Quantum Effects on Neutrino Parameters From a Flavored Gauge Boson
- Abstract:
Oscillation experiments have shown that, despite expectations,
neutrinos have non-zero masses and mix significantly, which may be
described model-independently using the unique dimension-five
Weinberg-Operator. Its structure can be restricted using flavor
symmetries, and radiative running effects can furthermore
significantly impact neutrino phenomenology due to the different
scales involved in their creation, detection, and mass generation. In
this work, we combine these paradigms, and consider the
renormalization group equations (RGEs) of the Weinberg-Operator in
flavor-nonuniversal gauge theories, such as the U(1)_(L_mu - L_tau)
extension of the Standard Model. We find that in such models, the new
gauge bosons induce novel terms in the beta-function of the neutrino
mass matrix at the one-loop level. These terms can raise the rank of
the mass matrix even at the one-loop level, and generate up to three
non-degenerate neutrino masses via RGE running only. This generalizes
the known RGE structure, and provides a new mass-generation mechanism.
- School Year: 3rd year (NAOJ)
- Name: Takumi Kakimoto (柿元 拓実)
- Title: The evolution of massive elliptical galaxies
- Abstract:
In the local Universe, the morphological properties of galaxies are
mainly divided into two (or three) groups, which is called the Hubble
sequence. One is ‘’spiral galaxies’’ which is like the Milky Way
morphology, and the other is ‘’elliptical galaxies’’ which has no
spiral arms. Under normal circumstances, galaxies produce stars from
gas material. However, massive elliptical galaxies display a lack of
star-forming activity and are primarily composed of old stars. ‘’Why
did these galaxies stop their star formation?’’ This is one of the
important questions in the galaxy formation and evolution field. To
solve this problem, we conduct the observation of the galaxies that
stop star formation at high redshift and try to confirm the physical
mechanism of quenching (suppressing their star formation) directly. In
this presentation, I will explore the formation scenario of a
quiescent galaxy in the early universe that I have uncovered.
- School Year: 2nd year (KEK)
- Name: Ruau Watanabe (渡辺 瑠合)
- Title: Compact NEG-coating Device and TiZrV films
- Abstract:
Non-Evaporable Getter (NEG) coating technology has been widely used in particle accelerator vacuum systems because it provides a
highly effective pumping speed and a low Photon Stimulated Desorption (PSD) yield. To take full advantage of these properties, it is
essential to have NEG coating cover as wide areas as possible, including complicated structures that have been difficult to coat.
For this purpose, we have been developing a compact, flange-mountable NEG-coating device.
We first characterized the plasma properties of this device by changing the sputtering parameters.
And then, under some optimum conditions, we have been elucidating the correlation between vacuum performance and crystal structures
of the films using SEM, EDS, and XPS. So far, we have successfully obtained a NEG film that is able to reach 10-9 Pa. The film
morphologies observed by SEM are comparable to those of the conventional NEG coating.
Furthermore, we found that the use of the TiZrV alloy target makes it easier to obtain the ideal composition ratio in the film.
Return to The 5th meeting from Monday, 10th to Wednesday, 12th March, 2025
https://sci.nao.ac.jp/MEMBER/kohri/05-KEK-NAOJ-JointSeminar.html
問い合わせ先: 郡 和範 (こおり かずのり)
https://sci.nao.ac.jp/MEMBER/kohri/
高エネ研–国立天文台連携セミナートップページ
https://sci.nao.ac.jp/MEMBER/kohri/KEK-NAOJ-JointSeminar.html