投稿者: YamashitaKazuyoshi

Radiation hydrodynamics simulations of massive star cluster formation

Speaker: Hajime Fukushima

Abstract:

Globular clusters (GCs) are believed to form in early galaxies, but the formation mechanism of GCs are still debated. In the star cluster formation, radiative feedback hampers star formation and increase of stellar density. Hence, the stellar feedback is a key factor in determination of star cluster properties. In this talk, I will review the star cluster formation and star formation quenching mechanisms, and introduce our recent simulations of massive star cluster formation and metal enrichment in the GC formation.

Mysterious fast radio bursts and the new radio telescope in Taiwan: BURSTT

Speaker: Tetsuya Hashimoto

Abstract:

Fast radio bursts (FRBs) are mysterious coherent radio pulses with millisecond timescales, most of which emerge from galaxies at cosmological distances. Uncovering the origin of FRBs is one of the central foci in astronomy. However, their origin is yet to be known due to the major observational challenge of FRBs: when and where they happen in the sky are unknown. Bustling Universe Radio Survey Telescope in Taiwan (BURSTT) is a new radio array dedicated to detecting mysterious FRBs in the nearby Universe. Within a few years, BURSTT will overcome this observational challenge with its unique capabilities of nearly all-sky monitoring (10,000 deg2) and accurate localization (< 1 arcsec), and none of the current FRB facilities have both of these capabilities. In this presentation, I will summarize the expected science cases with unique FRB samples of BURSTT. In contrast to the current FRB facilities, BURSTT will observe the same sky as multi-messenger instruments, including gravitational waves and neutrinos. This BURSTT’s design will maximize the chance of the simultaneous detection of multi-messengers or multi-wavelength counterparts, which would strongly constrain the FRB progenitor scenarios. BURSTT will provide a unique window into FRB applications from environments, progenitors, to cosmology.

Pursuing Sources of Cosmic High-energy Neutrinos

Speaker: Shigeo Kimura

Abstract:

Cosmic high-energy neutrinos are expected to be a smoking-gun signature to identify the origin of high-energy cosmic rays. IceCube experiment reported detection of cosmic high-energy neutrinos in 2013, the origin of which became a new mystery in astrophysics. In order to identify the cosmic neutrino sources, multi-messenger observational and analysis technics are now rapidly developing. In this talk, I will review the progress of high-energy neutrino astrophysics, discuss high-energy neutrino emission model in radio-quiet active galactic nuclei, and introduce our effort to identify neutrino sources using optical observational data.

Galactic Structure and Evolution: What 3D Magnetic Field Observations Are Revealing

Speaker: Mehrnoosh Tahani

Abstract:

Recent observations have significantly advanced our understanding of the three-dimensional (3D) structure and evolution of the interstellar medium (ISM). To fully comprehend ISM evolution, however, it is necessary to study interstellar magnetic fields, which play a pivotal role in the evolution of the galaxy and the formation of stars. Despite their importance, our understanding of magnetic fields in the ISM is limited due to significant challenges in observing them in 3D. In this talk, I will briefly discuss how we overcame the challenges in determining the 3D magnetic fields associated with giant molecular clouds. These 3D fields enabled us to propose step-by-step scenarios to explain the formation of these clouds, revealing previously undiscovered interstellar structure. Our approach involves a novel technique based on Faraday rotation measurements to detect the line- of-sight component of magnetic fields. We then integrate these line-of-sight measurements with plane-of-sky magnetic field observations to examine the 3D magnetic field morphology associated with the clouds. Finally, we employ Galactic magnetic field models to reconstruct the complete 3D magnetic field morphologies of these clouds, including their previously unknown direction. These 3D studies provide novel constraints on theories for the formation and evolution of star-forming clouds.

Extended Structure in Globular Clusters

Speaker: Pete Kuzma

Abstract:

Globular star clusters (GCs) are significant building blocks of the Milky Way’s (MW) Galactic halo. With typical ages of approximately 10 billion years, GCs are relics from the earliest stages of galaxy formation and are suggested to have contributed significantly to the halo assembly process. The current population of over 160 GCs may represent a mere fraction of the initial population of GCs, as the halo is rich in stars with chemical abundances suggesting they originate from GCs. An exciting development over the past 20 years has been the discovery that several MW GCs possess significantly extended structures, sometimes reaching out to a few hundred parsecs (corresponding to many half-mass radii). The types of features found range from axisymmetric tidal tails to large diffuse stellar envelopes. Such structures are indicative of mass loss, but our understanding of extended stellar structures, such as chemistry, kinematics and overall ubiquity, is currently incomplete apart from a very small sample. This is primed to change as upcoming large spectroscopic surveys commence and provide spatial coverage and depth that have been difficult to achieve until now. In this talk, I will explore the nature of extended GC structures and their role in the build-up of the Milky Way halo. I will explore before and after the Gaia revolution, both chemically and kinematically, and how future surveys will revolutionise our view of GCs and their peripheries.

Excursion beyond the Standard Model Physics – Gravitational Waves and Beyond

Speaker: Arnab Chaudhuri

Abstract:

The standard model of particle physics, even though very successful, however is incomplete. It fails to explain the origin of the matter-antimatter asymmetry, neutrino masses and have any suitable candidates for dark matter. Within the framework of the standard model electroweak phase transition is crossover in nature. Hence a lot of beyond the standard model theories have been established in both particle physics and cosmology to overcome these shortcomings. The recent results from NANOGrav have also established the existence of secondary or stochastic gravitational waves. In this talk, I will go through some models with the main focus being the creation of these stochastic gravitational waves due to a first order phase transition.

This talk will be primarily based on JCAP 01 (2018) 032, Phys.Rev.D 106 (2022) 9, 095016 and arXiv: 2404.10288 .

Observational study of high-mass star formation at the junction of filaments

Speaker: Kshitiz Mallick

Abstract:

Understanding high-mass star formation is an important pillar of astronomical research, due to the large impact of such sources on their natal environment. Various paradigms have been proposed for the formation of such stellar sources, with hub filament systems (HFS) having emerged as an important contender for understanding not only how massive stars form, but also the evolution of a molecular cloud as it collapses and fragments to form stars. In this talk, I present the results of my recent observational analysis of some high-mass star forming regions, carried out using molecular data cubes, complemented by other multiwavelength data. We discuss the complex nature of such star forming regions, the conundrums faced in analysis of hubs and filamentary structures, and the further work one needs to undertake to fully comprehend the connection between (high-mass) star formation and HFS.

* This presentation will be a joint session between the ALMA-J Seminar and the NAOJ Science Colloquium.

A Rogue Planet Hypothesis for the Formation of the Trans-Neptunian Solar System ―太陽系外縁の形成におけるローグ惑星仮説―

Speaker: Yukun Huang

Abstract:

Over the past two decades, our knowledge of the Solar System’s Trans-Neptunian region (often called the Kuiper Belt) has been gradually increasing. Observational surveys have greatly expanded the inventory of Trans-Neptunian Objects (TNOs), which are distant icy bodies thought to be relics from the giant planet formation era. In the distant Kuiper Belt beyond 50~au, several striking features seem to challenge our previous understanding of the early Solar System: 1) a very large population of objects in distant mean-motion resonances with Neptune, 2) a substantial detached population that are not dynamically coupled with Neptune’s effects, and 3) the existence of three very-large perihelion objects, known as Sednoids. I will demonstrate in this talk, that a super-Earth-mass planet temporarily present in the Solar System (referred to as a ‘Rogue Planet’), is able to create all these structures in the distant Kuiper Belt. Such a planet would have formed in the giant planet region and gotten scattered to a highly-eccentric orbit with a few hundred au semimajor axis with a typical lifetime of 100 Myr. Additionally, when examining the past history of the three Sednoids, I surprisingly find that all their apsidal lines were tightly clustered at 200° exactly 4.5 Gyr ago. This “primordial orbital alignment”, if confirmed true, strongly argues for an initial event that imprinted this particular apsidal orientation on early detached TNO population, and the rogue planet model could potentially explain this new phenomenon.

Inferring the evolution pathways and the explosion mechanism of core-collapse supernova through late-phase spectroscopy

Speaker: Qiliang Fang

Abstract:

Core-collapse supernovae (CCSNe) are considered as the final explosions of massive stars, following the depletion of the nuclear products in their cores. These catastrophe events are diverse in observation especially the chemical composition in the expelled material (ejecta), which implies varied mass-loss histories preceding the explosion. Despite over a century of discoveries, the mechanism responsible for the diversity in CCSNe, and its potential connection with the still-unresolved core-collapse process, is still a topic of active debate. In this talk, I will introduce the application of late-phase (nebular) spectroscopy of CCSNe to reveal these longstanding mysteries. Beginning with the fundamental concepts of CCSNe, I will provide an overview of the physical quantities that can be inferred from nebular spectroscopy. Next, I will demonstrate how the statistics analysis of nebular spectroscopy can be employed to constrain the properties of the progenitor, the dynamics of the ejecta, and their mutual relations. This investigation suggests massive stars leads to more aspheric and energetic explosions. Finally, I will introduce my future research plan, which aims to connect the diverse pre-SN activities discovered by recent transient surveys with the properties of their progenitors.

Circumgalactic Medium and Large Scale Structure at z=2 Traced by Lya Emission

Speaker: Haibin Zhang

Abstract:

In current pictures of galaxy formation and evolution, galaxies are closely related to their surrounding circumgalactic medium (CGM) and large scale structure (LSS). To investigate the CGM and LSS at high-z, I will introduce our “MAMMOTH-Subaru” paper series that study ~3300 Lyα emitters (LAEs) and ~120 Lyα blobs (LABs; luminous and massive LAEs) at z=2 selected with Subaru/HSC data. Our main results are: 1. We stack our LAEs to identify the faint Lyα emission in CGM (Lyα halo; LAH). Our LAH is detected till ~100 kpc at the 2σ level and likely extended to ~200 kpc. We show that more massive LAEs generally have more extended (flatter) LAHs. 2. We find that most (~70%) LABs locate in overdense environments. A unique protocluster region (~40*20 cMpc^2) contains 12 LABs, showing an extremely high LAB number density (>2 times higher than the SSA22 field). We calculate the angular correlation functions of LAEs and LABs, and suggest that LABs are more clustered and likely reside in more massive dark matter halos than LAEs. 3. We calculate the Lyα luminosity function at z=2 and demonstrate an observational approach to measure the cosmic variance. We find that our measurements cannot be explained by previous simulations, and that LAEs likely have a larger cosmic variance than general star-forming galaxies.