The KEK-NAOJ Joint Seminar
高エネ研–国立天文台連携セミナー
The 1st meeting on Friday, 1st Oct., 2021 at 10:00 -- 12:00
https://research.kek.jp/people/kohri/KEK-NAOJ-JointSeminar.html
[Abstract]
10:00 – 10:15 講演者: 津久井 崇史 (国立天文台 総研大5年)
Speaker: Takashi Tsukui (NAOJ, Sokendai 5th year)
Title: The measurement of galactic structures in a galaxy more than 12 billion years ago using the gas dynamics.
Abstract: Spiral galaxies observed in present universe have distinct internal structures:
supper massive black hole, dense stellar cluster known as bulge; a flat rotating disk;
and an extended dark matter halo. The cosmic averaged star formation is suggested
to peak at 10 billion years ago. It remains unclear when and how these structures
formed and evolved in the cosmic history. Analyzing the rotation velocity profile of
gas disk allows us to derive the baryonic (e.g., gas and stars) and dark-matter mass
distribution, which is powerful tool to investigate the internal structures of galaxies.
We have been establishing a method to derive the mass (distribution) of SMBH, bulge,
disk, dark matter halo in nearby galaxies using stellar and gas kinematics.
Recently, we investigated publicly available data in the ALMA (Atacama large millimeter/sub-millimeter array) archive
with the motivation of applying the method to further distant galaxies
(equivalent to further back in time in the universe). As a result, we discovered a rotating disk,
a central compact structure like a bulge, and spiral structure on the disk
in a galaxy at the redshift of 4.4 (over 12 billion years ago), long before the peak of cosmic star formation.
Spiral-arm formation requires disk structures which have been recently discovered by
ALMA at similar redshift of z=4 to 5. Although the disk formation epoch is still highly uncertain,
our result may indicate that spiral structure has formed in a very short period of time
after the disk formation, giving us a new question how the spiral morphology formed
in such a short period of time?
10:20 – 10:35 講演者: 伊藤 慧 (国立天文台 総研大5年)
タイトル：すばる望遠鏡で探る宇宙初期の大規模構造と銀河進化
アブストラクト:
宇宙には銀河の高密度領域である銀河団や低密度領域である ボイドと呼ばれる領域が存在する。
この大規模構造で異なる環境に存在する銀河 は、異なる性質や成長過程を持つことが知られている。
銀河進化の理解には、大規模構造と銀河の性質の関連を宇宙初期でも調査する必要がある。
そこで我々は 銀河団の祖先である「原始銀河団」の探査を約120億年前の宇宙において行って いる。
すばる望遠鏡によるHSC-SSPという大規模可視撮像サーベイを基に、これまでに原始銀河団
候補を約180領域発見した。本講演ではこの領域内に存在する 銀河の性質を特に静止系紫外光
に着目し調査した結果について紹介する。
Speaker: Kei Ito (NAOJ, Sokendai 5th year)
Title: Large-scale structure and galaxy evolution in the early universe revealed by the Subaru Telescope
Abstract: In the universe, there are dense regions of galaxies called clusters
and less dense regions called void. In the local universe, it is widely known that
galaxies in different environment have different properties and different
evolution. In order to understand the evolution of galaxies, it is essential to
understand the connection between the large-scale structure and galaxy properties
in the early universe. We are now searching for progenitors of clusters, called
"protoclusters" in ~12Gyrs ago. The optical imaging survey of the Subaru
Telescope, "HSC-SSP," has enabled us to find ~180 protocluster candidates.
In this talk, I would like to report on my studies investigating the properties of
galaxies in these protoclusters, mainly focusing on the rest-frame ultraviolet luminosity.
10:40 – 10:55 講演者: 滝脇 知也 (国立天文台 科学研究部助教)
タイトル：重力崩壊型超新星爆発で起こるニュートリノ振動
アブストラクト:
3種類のニュートリノに質量差があるせいで起こるニュートリノ振動は不思議な
現象と思われがちですが、実は簡単な量子力学の式で表されます。スーパーカミ
オカンデで明確な証拠が見つかり、梶田隆章教授はノーベル賞を受賞しました。
一方で非線形で非常に複雑な現象も起こります。超新星爆発が起こるような大質
量星の中で、ニュートリノが他のニュートリノと散乱し、その効果で起こる
ニュートリノの集団振動は、多くの研究が既になされていますが、まだ十分に理
解されていません。このニュートリノ集団振動は超新星の爆発メカニズムを考え
る上では欠かせないので、困難でも理論予測をする必要があります。
もしかしたら、このニュートリノ振動の研究は素粒子物理の発展に寄与する可能
性もあります。例えばこの研究でニュートリノがディラックタイプなのかマヨラ
ナタイプなのか決定できるかもしれません。今回は大学院時代を科学研究部で過
ごした佐々木宏和さんが主導してきたニュートリノ集団振動の研究を共著者であ
る滝脇が発表します。
Speaker: Tomoya Takiwaki (NAOJ, Division of Science, Assistant Professor)
Title: Neutrino oscillation in core-collapse supernovae
Abstract: The mass difference of the three flavor neutrinos induces a mysterious
phenomenon, which is called neutrino oscillation. A simple equation of
quantum mechanics derives the neutrino oscillation, and Super-Kamiokande
beautifully showed its evidence. On the other hand, in the environment
of the center of the massive star, the high neutrino density leads to
collective neutrino oscillation since we cannot ignore the scattering of
the neutrino by another neutrino. The process of the collective
neutrino oscillation is highly non-linear, and we have not fully
understood the phenomena. Since that is an essential part of the
mechanism of core-collapse supernovae, we need to solve this complex
problem. Perhaps the study may help us understand particle physics,
e.g., determining the neutrino type Majorana or Dirac. We review the
recent works on this topic, which Hirokazu Sasaki has led, an alumnus of
the Division of Science.
11:00 – 11:15 講演者: 加藤 晶大 (高エネ研 素粒子原子核専攻・CMB実験 総研大3年)
タイトル: 波長可変赤外レーザーを使ったLiteBIRD衛星の宇宙線ノイズ評価試験
アブストラクト:
インフレーションモデルを検証することを目的の一つとするCMB偏光観測衛星
LiteBIRDを20年代後半に打ち上げる計画が進行中である。衛星による観測は地上
での観測に比べて大気によるノイズの影響を受けない点や大スケールの観測がで
きる点で優れているが、最新のCMB観測衛星Planckによって宇宙線によるノイズ
が報告されている。LiteBIRDの目標達成のためには、宇宙線によるノイズを踏ま
えた性能評価が必要となる。ここでは、LiteBIRDに搭載予定の検出器と赤外線レ
ーザーを使った宇宙線ノイズ評価試験の構想を紹介する。
Speaker: Akihiro Kato (KEK, IPNS, CMB experiment, Sokendai 3rd year)
Title: Characterization of cosmic ray noise of LiteBIRD satellite using a tunable infrared laser
Abstract: A plan is underway to launch the CMB polarization observation satellite
LiteBIRD in the late 20s. The main objective of LiteBIRD is to test cosmic inflation models.
Satellite observations are superior to ground-based observations because
they are not affected by atmospheric noise and can observe large-scale
fluctuations. However, the latest CMB satellite, Planck, has reported noise due to cosmic
rays. To achieve the goal of LiteBIRD, we need to examine the performance of LiteBIRD,
considering the noise caused by cosmic rays. In my study, I will describe a conceptual design
of a cosmic ray noise characterization system with a tunable infrared laser for the detector
to be installed in LiteBIRD.
11:20 – 11:35 Speaker: Bajpai Rishabh (KEK, Sokendai 4th year)
Title: Gravitational Wave Detector and Study of Cryogenic Technical Noise in KAGRA
Abstract: In 1916, Albert Einstein predicted the existence of gravitational waves after the formulation of
General Theory of Relativity. Gravitational waves are ripples in the curvature of space-time which
propagate at the speed of light. The current generation Gravitational Wave detector are ultra-sensitive
interferometer that detect displacements of the order of 10^(−19) m/rHz making it essential to minimize
environmental displacement noise. KAGRA (Kamioka Gravitational-Wave Detector) is a second-generation
GW detector in Japan. One of the unique features of KAGRA is the cryogenic operation of the four main
mirrors (23 kg artificial monocrystal sapphire test mass) to reduce the thermal noise. The mirrors are
cooled down inside a cryostat by four pulse-tube cryocoolers. Monitoring the vibration inside cryostat
(cryogenic technical noise originating from cryocooler operation) is important for optimum noise
performance of the detector. We developed a compact cryogenic accelerometer prototype
with a Michelson interferometer readout for this purpose. In this presentation I will talk about the principle
of current gravitational wave detector and how different noises affect the detector sensitivity,
with focus on vibration noise generated from the KAGRA cryogenic system.
11:40 – 11:55 講演者: 郡 和範 (高エネ研 理論センター准教授)
タイトル: 天文学と高エネルギー物理学をつなぐ初期宇宙のインフレーション
アブストラクト:
宇宙初期にインフレーション期と呼ばれる、ビッグバン宇宙より激しく膨張する時期がありました。
インフレーションは素粒子の一種である未発見のスカラー粒子であるインフラトン場が引き起こしたと
理論的に考えられています。そのエネルギーは凄まじく、約1016 GeVという素粒子の力の大統一理論のスケールで、
宇宙年齢が約10-38秒あたりで起こったのではないかと予想されています。このことはCMBの衛星実験Planck
のデータとも無矛盾です。インフラトン場の量子揺らぎが、宇宙の密度ゆらぎを生み、すべての
宇宙の物質の構造の種となったことが理論的に予言されています。そのため、インフレーション研究の進展は、
天文学と高エネルギー物理学をつなぐ鍵となることが期待されます。今回、インフレーション理論
の簡単な解説と最近の進展をお話しします。
Speaker: Kazunori Kohri (KEK, Theory Center, Associate Professor)
Title: Theory of the Inflationary Universe: A unique bridge between astronomy and high-energy physics
Abstract: In the early Universe, there existed an inflationary epoch in which
the Universe expanded exponentially. The speed of the expansion in
this epoch was much more rapid than that of the big-bang Universe.
Theoretically we believe that an undiscovered scalar field called
"inflaton field" induced inflation, which occurred at around cosmic time
being 10-38 second with the energy scale ~ 1016 GeV. This is
consistent with the recent observation for temperature fluctuations
and polarizations of the Cosmic Microwave Background reported by the
Planck satellite. In theoretical models of inflation, we predict that
cosmological density fluctuations were produced by quantum
fluctuations of the inflaton field during inflation, which become
seeds of any structures formed in the present Universe through the
gravitational instability. Therefore, we expect that research on the
inflationary Universe becomes one of the unique bridges between
astronomy and high-energy physics. I will briefly review a basic
concept of inflation and report recent topics related to inflation.
問い合わせ先: 郡 和範 (こおり かずのり)
https://research.kek.jp/people/kohri/
