投稿者: Yuko Matsushita

Quasars as high-redshift cosmological probes

speaker: Giada Bargiacchi

Abstract:

Quasars (QSOs) have the potential to be the next rung of the cosmic distance ladder beyond type Iasupernovae (SNe) as they can be turned into standardizable candles through their non-linear X-ray to ultraviolet (UV) luminosity relation. Indeed, we have verified that this relation is intrinsic to QSO physics and not artifact of selectonbiases or redshift evolution by applying the statistical Efron & Petrosian method. Extending the cosmological analyses with high-redshift data is the key to distinguishing between different cosmological models that are instead degenerate at low redshifts, and allowing a better constraint on a possible dark energy (DE) evolution. We use the most updated QSO sample combined with SNe and, when possible, baryon acoustic oscillations (BAOs) data to test different kinds of cosmological models. We find that a joint analysis of QSO+SNe with BAO is only possible in the context of a flat Universe. We also find that the matter component, ΩM,0 , is fully consistent with ΩM,0 = 0.3 in all the data sets assuming a flat ΛCDM model. Yet, all the other analysed models show a statistically significant deviation at 2- 3 σ from this prediction by making use of the SNe+QSO+BAO sample. In the models where the DE density evolves with time, the SNe+QSO+BAO data always prefer ΩM,0 > 0.3, w0 < −1 and wa greater, but statistically consistent, than wa = 0. This DE phantom behaviour is mainly driven by the contribution of SNe+QSOs, while BAO are closer to the prediction of the flat ΛCDM model

Predicting the redshift of gamma-ray loud AGNs and GRBs using Supervised machine learning Active galactic nuclei

speaker: Aditya Narendra

Abstract:

(AGNs) are very powerful galaxies characterized by extremely bright emissions coming from their central massive black holes. Knowing the redshifts of AGNs provides us with an opportunity to determine their distance to investigate important astrophysical problems, such as the evolution of the early stars and their formation, along with the structure of early galaxies. However, redshift determination is challenging because it requires detailed follow-up of multiwavelength observations, often involving various astronomical facilities. In this presentation I will discuss about the methodology developed by our team, where we apply a powerful machine learning technique called SuperLearner to estimate the redshift of gamma-ray loud AGNs from the Fermi 4th LAT catalog (4LAC). Using the 4LAC’s observed properties we train the machine learning model on 1112 AGNs, obtaining a correlation of 75% between the predicted and observed redshift. We also explore the application of an imputation method called Multivariate Imputation by Chained Equations (MICE), using which we impute missing data for 24% of the catalog and proceed to investigate its effects on the redshift estimation. Further, we also explore the application of bias corrections and feature engineering for improving our results. Finally, we provide predicted redshift for 300 BL Lacertae Quasars of the 4LAC using our methodology. Similar method is applied to GRBs. I will present the results for GRBs as well.

Molecular Dynamics Simulations Explore Dust Monomer Interactions: An Extension of the JKR Adhesion Model

speaker: Yuki Yoshida

Abstract:
Dust is the main material of planets, and grows into planets. The minimum unit of dust is considered to be a sphere 0.1 um in size called a monomer. Monomers grow to cm size by collisional coalescence due to intermolecular forces. However, the growth process is not understood well. The collisional growth process has been studied by laboratory experiments and numerical calculations. In numerical calculations, the JKR theory, which gives the interactions of adhesion, rotation, sliding, and twisting between monomers, is used as the monomer interaction. However, it has been suggested that actual monomers have viscosity so that a part of the kinetic energy of the monomers is converted to that of the molecules (Tanaka et al. 2015). Therefore, it is necessary to extend the JKR theory based on molecular physics.We investigated monomer head-on collision to clarify the adhesion interactions by performing molecular dynamics (MD) simulations and investigated the coeffecient of restitution. We then performed simulations with temperatures and impact velocities to obtain the dependence on the coeffecient of restitution. In this talk, I will present our MD simulation and our recent studies. We found that the coefficient of restitution decreases when the impact velocity is higher than a certain value or when the temperature is higher. In addition, the coefficient of restitution is significantly smaller for higher impact velocity compared to the JKR theory, indicating that collisional physics and the JKR theory are qualitatively different. We, therefore, attempted to modify the JKR theory using the dissipative model of Krijt et al. (2013). We will present these results in detail and propose a new extended theory of JKR theory.

Characterizing three serendipitously detected CO emitters

speaker: Shuo Huang

Abstract:
I present photometry and SED analysis of three serendipitously detected CO emitters in the SSA22 protocluster field. The single-line CO detection in ALMA band 3 suggests redshift of ~1.4 of two sources and 1.7 of the third source. To examine the redshift and investigate their properties, I perform multiband photometry and SED analysis. All these three sources have Spitzer IRAC counterpart, two of them have MIPS 24 um and/or Herschel detection. Then I check the single-line CO redshift with photometric redshift from SED. I will also discuss the extracted physical properties such as stellar/dust mass and SFR.

High Dimensional Statistical Analysis of ALMA Map of NGC 253

speaker: Tsutomu Takeuchi

Abstract:
In astronomy, if we denote the dimension of data as $d$ and the number
of samples as $n$, we often meet a case with $n \ll d$. Traditionally, such
a situation is regarded as ill-posed, and there was no choice but to throw
away most of the information in data dimension to let $d < n$. The data
with $n \ll d$ is referred to as high-dimensional low sample size (HDLSS).
To deal with HDLSS problems, a method called high-dimensional statistics
has been developed rapidly in the last decade. In this talk, we introduce
the high-dimensional statistical analysis to the astronomical community.
We apply two representative methods in the high-dimensional statistical
analysis methods, the noise-reduction principal component analysis (NRPCA) and regularized principal component analysis (RPCA), to a spectroscopic map of a nearby archetype starburst galaxy NGC~253 taken by the Atacama Large Millimeter/Submillimeter Array (ALMA). The ALMA map is a typical HDLSS dataset. First we analyzed the original data including the Doppler shift due to the systemic rotation. The high-dimensional PCA could describe the spatial structure of the rotation precisely. We then applied to the Doppler-shift corrected data to analyze more subtle spectral features. The NRPCA and RPCA could quantify the very complicated characteristics of the ALMA spectra. Particularly, we could extract the information of the global outflow from the center of NGC~253. This method can also be applied not only to spectroscopic survey data, but also any type of data with small sample size and large dimension.

Applications of Hydrodynamical Simulations for Clustering of Emission Line Galaxies

speaker: Ken Osato

Abstract:
In order to address the structure formation and evolution at the distant Universe, emission line galaxies (ELGs) are suitable targets for upcoming spectroscopic surveys (PFS, Euclid, DESI). Since the strong emission line is sourced by massive OB-type stars, in general, ELGs are star-forming young galaxies. Thus, the clustering nature of ELGs is expected to be quite different from that of luminous red galaxies, which are widely studied in the past spectroscopic observations. In order to address clustering properties of ELGs, we utilise galaxy formation hydrodynamical simulations: IllustrisTNG. We have developed the method to simulate emission line intensity with stellar population synthesis code PEGASE-3. In simulations, we can directly investigate the relation between properties of ELGs and host halos and measure the cosmological statistics, e.g., correlation function. First, we measure the halo occupation distribution (HOD) and find the signature of infalling distinct halo contribution as suggested by semi-analytic simulations. Next, we meaure the projected correlation function and infer HOD parameters with the correlation function. Finally, we discuss whether the true HOD can be reproduced from the projected correlation function measurement.

Climates of terrestrial exoplanets with 3D GCM

speaker: Takanori Kodama

Abstract:
Many exoplanets have been detected since 1995. Some of them are expected to be rocky planets with Earth-like bulk composition within the habitable zone, which is defined as the region around the central star where liquid water on the planetary surface remains stable for a long term. New space telescope observations are planned to reveal the characteristics of the atmosphere of exoplanets. In the next decade, such potential habitable exoplanets will be the primary targets for observation of life on exoplanets. Classically, the planetary atmosphere has been investigated with 1D radiative-convective equilibrium model. Recently, the climate for exoplanets in the habitable zone has been estimated with 3D general circulation models (GCMs) to capture the non-uniformity.
In this talk, I will review the habitability of terrestrial exoplanets from the viewpoint of 1D and 3D climate models. And I will show our recent studies where we focus on the distribution of water on the surface and in the atmosphere. We found that habitability is strongly depended on the surface environment. Finally, I will introduce an application with NICAM(Non-hydrostatic ICOsahedral Atmospheric Model), known as a global cloud resolved model, and will discuss the difference between a classical GCM and a global cloud resolved model.

Atmospheres of sub-Neptune-sized exoplanets in contact with magma ocean

speaker: Seo Chanoul

Abstract:

Sub-Neptunes are small exoplanets (Planetary radius = 2~3 Earth radius) with voluminous atmospheres and are important targets of future recent and upcoming transit spectroscopy. However, the framework to relate their atmospheric properties to their hidden interior and the formation pathway has not been well established. As the mass of sub-Neptunes is dominated by the silicate core, their atmospheres are likely to be affected by the reaction with the underlying magma (i.e., molten rock) if they exist. Thus, we study the atmospheric composition of sub-Neptunes in the presence of magma ocean using an equilibrium model of the Fe-Si-Mg-H-C-O system with Fe-FeO-Fe2O3 magma redox buffer. We find the nebula-origin atmospheres can be highly oxidized to form H2O-dominated atmospheres when the accreted amount of volatile is moderate and(or) the iron core fraction is small. We show how the two observable atmospheric parameters, H2O fraction and atmospheric C/H ratio, in the combination of the measurement of mass and radius, can infer the initial magma redox state and composition of accreted volatiles (nebula gas and pure ice). The high solubility of H2O into magma and the small solubility of C-bearing species enrich C-bearing species in the atmosphere, which could be used as an indicator of the presence of magma-atmospheric reaction. Such properties of atmospheres may also provide a way to distinguish several suggested formation scenarios of small planets around M-type stars.

MHD simulation of cluster formation in clumps

speaker: Kinoshita Shinichi

Abstract:

It is well known that stars are often born in clusters. Thus, understanding cluster formation is very important to grasp the general picture of star formation and the evolution of the galaxy. In recent studies, the cluster-forming clumps are considered to be the parent objects of clusters (Lada & Lada 2003). Cluster-forming clumps tend to exhibit complex velocity structures with several velocity components. One of the hypotheses to explain these velocity fields is the collisions of clumps (e.g., Higuchi et al. 2010). Clump-Clump Collision is proposed as a possible mechanism for triggering the formation of clusters. On the other hand, some studies show that complex velocity structures can be explained by the infalling motion of a single clump with rotation (e.g., Shimoikura et al. 2016). Some expect that such a dynamical infall is a common phenomenon for cluster-forming clumps. In this way, several hypotheses have been proposed, and the formation and evolution processes of clusters still remain unclear.
In this talk, I will show some results of the MHD simulation of cluster formation. We investigated the cluster formation in a single clump infalling with rotation. We will discuss the dynamical evolution of clumps and the properties of dense cores.

Pseudo-observation of spiral galaxies focusing on depolarization based on MHD simulation

speaker: Yuta Tashima

Abstract:

It is known that the average magnetic field strength of spiral galaxies is about a few micro G, but the structure of the global field is still unknown. Since observables are integral values ​​on the line of sight, it is difficult to obtain a three-dimensional structure. Therefore, we aim to clarify the relationship between the radiation field and the spatial distribution of physical quantities through pseudo-observations using global three-dimensional magnetohydrodynamics (MHD) simulation results. In particular, we are focusing on the depolarization effect, which is important in the meter-wave band, to verify the polarization model and to identify the emission region. As a result, we found that the spiral polarization projected on the screen is made up of overlapping magnetic flux tubes of different heights from the equatorial plane. It suggests that the traditional classification of global magnetic fields has difficulty reproducing the global structure of the magnetic fields. In addition, we have examined the possibility of separating this magnetic tube using the properties of beam depolarization. I will also report on this result.