投稿者: Yuko Matsushita

Dense Cores Embedded in 70µm-dark High-mass Clumps: CMF and Fragmentation

speaker: Kaho Morii

Abstract:
The very early evolutionary stage of high-mass star and cluster formation is a key phase for understanding how the progenitors of stars form and evolve. We have conducted the ALMA Survey of 70 µm Dark High-mass Clumps in Early Stages (ASHES) toward thirty-nine cold regions with massive, dense molecular gas, which are thought to be the ideal sites to investigate the early phase of high-mass star formation. The high-resolution (~1.”2) and high-sensitivity observations mosaicked by ALMA succeed in revealing the internal structure of infrared-dark clouds and the unprecedented amount of 839 cores. This is the largest sample of cores in IRDCs observed with ALMA so far. In this talk, I will present prestellar core mass function (CMF) with the comparison with protostellar CMF and Salpeter’s IMF, and the fragmentation properties compared with Jeans fragmentation.

Elemental Abundance Ratios and Origin of Very High (Fe/O) in Extremely Metal-Poor Galaxies

speaker: Kuria Watanabe

Abstract:
Extreme metal-poor galaxies (EMPGs) are low metallicity, and young.
Elemental abundance ratios of EMPGs provide insight into star formation in the early stages of galaxy formation. Although the metallicity of EMPGs is less than 10 % of solar, several EMPGs with [Fe/O] as large as the solar abundance are reported.
Since EMPG is a young galaxy, type Ia supernovae have probably not yet occurred.
Therefore, we investigate the possibility that pair-instability supernovae (PISN) and hypernovae (HN) with high explosion energy produced rich iron. Using our initial mass function and the yields of previous studies, we develop the models of the chemical evolution of galaxies and compare them to observations. We focus on S and Ar, which are abundant in PISN. Since the [S/O] and [Ar/O] in EMPG are smaller than in the PISN model, we suggest that the origin of Fe in EMPG is not PISN.
We also study the effects of the supernova explosion energy and the mixing & fallback model (Umeda & Nomoto 2002). We calculate the yields of CCSN and HN using the yield calculation code for the core-collapse supernova (CCSN) model. Using the yield with varying effects of the mixing & fallback model, we develop a model of the chemical evolution of galaxies and introduce the results compared to observations.

Early Galaxy Formation Near and Far Probed with SDSS and JWST Data

speaker: Moka Nishigaki

Abstract:
Extremely metal poor galaxies (EMPGs), which are defined by the gas-phase metallicity of < 0.1 Zsun, are important to understand the early phase of galaxy formation. Although EMPGs are actively investigated over decades, there are no EMPGs with metallicities below < 0.01 Zsun found so far, which is called the metallicity floor. In addition, the physical origin of EMPGs in the local universe are not fully understood. We search for the metal-poor galaxy candidates in the local universe below the known possible metallicity floor of < 0.01 Zsun, selecting photometric candidates by broadband color excess and machine-learning techniques with the SDSS photometric data. We remove stellar contaminants from the photometric candidates by shallow spectroscopy with Seimei and Nayuta telescopes. We then conduct deep spectroscopy with Magellan/MagE for faint [OIII]4363 lines and confirm that three candidates are EMPGs with 0.05-0.1 Zsun. We also discuss the physical origin of EMPGs from their clustering and chemical properties. Extending the broadband color excess technique to a high-z EMPG search, we select 17 candidates of z ~ 4–5 EMPGs with the deep near-infrared JWST/NIRCam images obtained by Early Release Observations (ERO) and Early Release Science (ERS) programs. We find galaxy candidates with negligible [OIII]4959,5007 emission weaker than the local EMPGs and known high-z galaxies, suggesting that some of these candidates may fall in 0–0.01 Zsun, which potentially break the lowest metallicity limit known to date.

Observational Constraints on the Dust Albedo Spectrum in a Protoplanetary Disk

speaker: Tomohiro Yoshida

Abstract:
Planets and planetary cores are formed by the coagulation of dust grains in a protoplanetary disk. Therefore, it is crucial to constrain the dust composition. Such dust grains in the disk midplane are observed at mm wavelengths. However, it is challenging to observationally constrain the composition directly because the mm-wavelength continuum emission of the dust does not show features as seen in infrared wavelengths. Meanwhile, recent observations and theory show that scattering significantly affects the emission even in the mm-wavelengths when the grain size is large. Since the scattering albedo as a function of wavelength (“albedo spectrum”) depends on the dust composition and grain size distributions, the constraints on the albedo can provide a hint on the nature of the dust. However, observational constraints on the albedo have been also difficult due to its degeneracy with temperature. In this talk, we propose to use the pressure broadened CO line wings, which are optically thin and trace the deepest region of the disk, as a thermometer of the disk midplane. We apply the method to ALMA archival observations of CO J=2-1 and 3-2 lines in the inner region of the TW Hya disk, and derive the mm-wavelength albedo spectrum for the first time by combining observations of other bands. We also discuss the constraints on the dust properties.

The Burst Observer and Optical Transient Exploring System in the multi-messenger astronomy era

speaker: Alberto J. Castro-Tirado

Abstract
The Burst Observer and Optical Transient Exploring System (BOOTES) was first designed as an asset of autonomous telescopes that started to be deployed in 1998, taking 24 years to be fully developed around the Earth. Nowadays BOOTES has become a global network of robotic telescopes, being the first one present in all continents, as of 2022.
I will present the different subsystems of the BOOTES network and review its achievements over the last two decades regarding follow-up observations of high energy transient events. Moreover, considering the advent of neutrino and gravitational wave detectors, I will discuss the role of the network within the framework of multi-wavelength astrophysics.

Light curves of electron capture and low mass Fe core collapse supernovae

speaker: Masato Sato

Abstract:
Stars with M<8Msun become white dwarfs in their last moment. Stars with M>10Msun evolve to Red Super Giant (RSG) or Wolf-Rayet and explode as Fe core collapse supernovae (FeCCSNe). The last moment of the M~8-10Msun is a one of the last unknown pieces of stellar evolution understanding. They make O, Ne, and Mg core at their center in the later phase of evolution. They are theoretically predicted to evolve to Super Asymptotic Giant Branch (SAGB) and finally become white dwarfs or explode as electron capture supernovae (ECSNe). However, mass range to become SAGB is not accurately estimated. Moreover, there are no supernovae which clearly identified as electron capture origin so far. SN2018zd were observed and proposed as an ECSN recently (Hiramatsu et al. 2021). However, it is also proposed as a FeCCSN (Callis et al. 2022) and common understanding is not obtained so far. Therefore, the clear identification of ECSN-like supernovae like SN2018zd is highly required. Although Kozyreva et al. (2021) revealed the bluer plateau for ECSN than FeCCSN, they didn’t include circumstellar material (CSM) interaction. However, recent observations and studies revealed that most of the supernovae have CSM before explosion. Therefore, the realistic characteristics of the ECSN light curves and the distinguishing method of it aren’t revealed.
We conducted numerical calculation of the light curves of low-mass FeCCSN and ECSN using multi-dimensional radiation hydrodynamical code STELLA (Blinnikov et al. 2000). RSG and SAGB progenitor models are taken from Sukhbold et al. (2016) and Tominaga et al. (2013) respectively. We include the CSM interaction into calculation using the method of Moriya et al. (2018).
We investigated the characteristics of the ECSN light curves comparing to low-mass FeCCSN. As a result, the bluer plateau for ECSN than FeCCSN is confirmed if CSM is not included and even if they are bolometrically degenerated. Moreover, as a preliminary result, the redder and fainter delayed shockbreakout is shown for ECSN than FeCCSN if CSM with high mass loss rate(~1e-2Msun/yr) is included. With low mass loss rate(~1e-4-6Msun/yr), bluer plateau for ECSN still can be seen. In the talk, we will introduce the progenitor models and resulting light curves in the talk.

Observational research of fragmentation process in nearby star-forming regions

speaker: Kousuke Ishihara

Abstract:
In the star formation process, molecular clouds hierarchically form dense structures by collapsing and fragmentation, then eventually leading to protostars. The scale at which fragmentation occurs is considered to contribute to the formation of stellar systems such as clusters and multiples. The most basic case is thermal Jeans fragmentation, which is determined by the balance between self-gravity and the pressure gradient due to thermal motion, and the expected characteristic fragmentation scale is called thermal Jeans length. Comparing with the core separation distribution and Jeans length provides a clue to the fragmentation process from clumps to cores. We have analyzed ALMA data (spatial resolution: ∼ 1000 au at 3 kpc) for 30 high-mass star-forming regions. As a result, we found a characteristic peak at ∼ 6000 au, which is comparable to the Jeans length. We have also confirmed that the result is robust even if considering observational biases due to differences in spatial resolution and mass sensitivity. In this talk, I introduce preliminary results of a similar analysis applied to dense cores in nearby star-forming regions. I obtained separation distribution by applying a Minimum Spanning Tree to the core coordinates in core catalogs obtained from the Herschel Gould Belt Survey. The results show a variety of distribution shapes with peaks at >10000 au in each region. The peak separation was found to be about 0.1 times the Jeans length in all regions. This may indicate that dynamical processes such as cloud-scale gravitational instability are important in the core formation process.

Towards an accurate cluster cosmology with photometric galaxy surveys

speaker: Tomomi Sunayama

 

Abstract:

Galaxy clusters are the most massive gravitationally self-bound objects in the Universe. These clusters form at the rare high peaks of the primordial density fluctuations, and they subsequently trace the growth of structure in the Universe as they grow in mass and abundance. As such, clusters constitute a natural cosmological probe for constraining the properties of the primordial fluctuations as well as cosmological parameters including the nature of dark energy. Clusters are, however, also known to be susceptible to many systematics such as selection biases and projection effects.We develop a new analysis pipeline which is full forward modeling of cluster observables (abundance, clustering, and lensing signals) with an empirical model for the projection effects (i.e., interloper galaxies along the line-of-sight are misidentified as genuine members of the cluster). The projection effects alter the mass-observable relation as well as boost the amplitude of clustering and lensing signals due to the anisotropic distribution of optical clusters. We validate our model on simulations and then apply it to the SDSS redMaPPer cluster catalog whose result favors low Omega-m and high sigma8. We discuss possible implications using Subaru HSC lensing measurements.

A new perspective on cosmology through Gamma-ray Bursts and Supernovae

speaker: Biagio De Simone

Abstract:
The state of the art of modern cosmology considers the LambdaCDM model as the standard paradigm for describing the structure and the evolution of the universe. Despite the wide success of this model, there are still many open problems on the list, in particular the Hubble constant tension. This is the discrepancy, in more than 4 sigma, between the value of the Hubble constant estimated through the local probes and the value of the Hubble constant inferred from the Cosmic Microwave Background. Supernovae Ia (SNe Ia) are able to cast more light on this open issue but, given the observational limitations, can be observed only up to redshift 2.3. New standardizable probes are needed, and in this perspective Gamma-ray Bursts (GRBs), being a class of excellent standardizable candles, gain a central role in the current and future analysis. In this talk, I will give a summary of modern cosmology and I will explain how the standard candles, such as Supernovae Ia, in combination with the Gamma-ray Bursts can cast more light on the open problems of modern cosmology.

The James Webb Space Telescope (JWST): Successful Commissioning and First Scientific Results

speaker: Eiichi Egami

Abstract:
After the successful launch and nearly flawless commissioning, the James Webb Space Telescope (JWST) has started to produce exciting results rapidly, In this talk, I will present a brief overview of the commissioning process and a selection of exciting first scientific results covering a wide range of topics, from exoplanets to high-redshift Universe. I will especially focus on the JWST Advanced Deep Extragalactic Survey (JADES) and its recent discoveries of the most distant galaxies at z>12 with spectroscopic confirmation.